I thought all romulan warbirds have that configuration.. warbirds have low defense and high offense. Or there is a way to have high defense (i mean hull or shield strenght, for example) and offense in a romulan warbird??
Well, I used to run a DD as a tank. The trick is the console from the valdore. It turns your energy weapon damage into shield heals. The more outgoing energy damage, the better the heals. So, if you can also use either 2EPTS and 2EPTW abilities to cycle through as often as possible, or 1 EPTS and 1 EPTW with A2B, you can keep shield heals and extra resistances going constantly. Use Science team for instant heals, or transfer shield strength for extra buff and slow heal if you have high aux power. You could use EPTA instead of weapons, but with the console from the valdore, you might want the EPTW to increase damage output and get a little extra shield healing as well.
Lots of good advice in this thread... and some... not so good advice.
I run a Reman tac toon, and as soon a the Scimitar came out, I got out of my stock Ha'feh, stopped saving for a fleet Mogai, and got my butt into a Scimi. I went boom. A LOT. I have never flown a ship that exploded more in my life (except my first time in my Ha'feh. I learned the meaning of the phrase NEED MOAR SHIELDS very well that week). I thought it was the ship. And I was right. Then they updated a few things on the Scimitar, reduced it's bugged to high heaven bleed, and altered some of the kersplosion mechanics on it.
I still went boom plenty. I realized it wasn't the ship, it was me. So... I did what any good player does. I bmw'd, then changed up my tactics.
If you're going to run the Scimi as a gunship, you need to realize three things.
1) You will hit HARD. Like dropping a freakin planet on your target hard.
2) You will NEED to keep things in your foward arc. If you can't do this, run beams.
3) You will have a harder time staying alive than a beamboat. It's not impossible (far from it), but it's harder.
Now once you realize these three things, we can move on to the next part of survival in a cannon scimi. There are a few things you should do that will make it a hell of a lot easier to stay alive in a cannon scimi.
1) Always always ALWAYS cycle EPtS1. You should have 100% uptime on that ability. That ALONE will increase your survival chances by a good 30-40%. Why? Think about what it does. First off, it's a quick shield heal. Not horribly strong, but it's useful. Secondly, it increases your shield power. That increases your shield regen and your shield damage resistance. Thirdly, it adds even MORE damage resistance to your shields (on top of what the boosted shield power gives you). Suddenly, your shields shouldn't be nearly as squishy as before.
2) Cycle Tac Team. The shield redistro from tac team combined with EPtS1 will make your ship very difficult for NPCs to kill. When using Tac team, the enemy is suddenly fighting the shield strength of all 4 facings, PLUS the regen from all 4 of those facings. And when your tac team is on cooldown, for those 5 seconds, you should be constantly manually redistributing your shields. Then you hit Tac team again and get back to killing things.
3) Cloak copiously. You have the Scimitar battle-cloak. ABUSE IT. If things get too fugly, hit a singularity jump, hit Evasive Maneuvers, get the hell out of dodge, and then cloak. Come back around, decloak, and chastise whatever it was that made you cloak in the first place.
4) Engineering Team. One of the biggest issues with Scimitars nowadays is shield bleed. According to the devs, it's fixed, but there are times when my Scimi still takes a stupid amount of bleed damage from hits (despite having two mk XII fleet neutroniums). And it's during those times when I hit ET2 and heal 8400 hull. It's quite nice. And now that it's no longer on a shared CD with Tac Team, staying alive is even easier than before.
5) If you're still having issues with your shields, Transfer Shield Strength is a great additive to EPtS1. It gives a low insta shield heal, but it then gives a HUGE bonus to shield regen, and a wonderful bonus to shield resilience. It also lasts for 15 seconds, during which it constantly heals your shields. Very useful.
6) Last but certainly not least, Hazard Emitters, Hazard Emitters, Hazard Emitters, Hazard Emitters. They are the number one method for dealing with the Borg. They're a relatively strong HoT, they cleanse plasma burns (frak the borg and their plasma), and they can be used on not only yourself, but an ally if necessary. Take into account the new Mirror Hakeev DOff, and HE are suddenly just that much more effective.
With that out of the way, let's look at your equipment.
The Jem'hadar mk XI set is nice. It really is. But as ESTF gear goes, it's sub-par. The deflector blows. The shields are ok, but they are actually kinda sub-par for ESTF usage, simply because they only have a 10% resistance to plasma damage. The engines are good, a nice hold-over until you can get better ones.
Now if you had access to large amounts of dil and omega marks, I would say get the mk XII assimilated engines and deflector, and then the mk XII MACO shield (that thing... is insane. 30% resistance to plasma along with the equivalent of capx2 mod AND boosted regen). That would make you more or less invincible against the Borg.
But I am guessing you don't have access to such... expensive gear or probably don't have the resources to acquire it, so I will instead recommend the following:
1) Keep the Jem engines. They work great until you can get assimilated engines or something else just as good.
2) Get a Positron Deflector Array. Preferably mk XI or better, preferably with at least one [SIF] and one [Stl] mod. That will greatly boost your hull and shield hit points. Make you tankier. On the off chance you can get a mk XI purple with [SIF], [Stl], AND [Em] mod for less than 7 mil ECs, that would be even better. But I would recommend just getting a Positron Deflector Array mk XI [SIF] [Stl]. Last I checked, they were going for ~250k ECs on the exchange.
3) Get a new shield. Preferably one more suited to ESTFs. My recommendation would be a Resilient Shield Array mk XII [Pla] [Cap] [Reg] or the same thing in mk XI. That will VASTLY out-tank your Jem shields. It will take less damage from the Borg, and will have a higher capacity and higher regen. It will also keep the bleed protection provided by virtue of being a resilient shield.
I can tell you for a fact, there is no problem at all with having your LtCmdr Uni to tac. I have it more or less locked there, and my survivability is still great. I can deal insane levels of damage, and tank quite well. There is no reason at all why you can't do the same. Just takes a little practice, some patience, a lot of dying, and learning. And when everything falls into place... let's just say the NPCs will suffer.