Aux powered cannons are supposedly an option that can be moved to other ships, and that you can have multiple copies of. Subject to change though.
That said, the only Fed ship with the ability to utilize the aux cannons is the Defiant and the Dreadnought. Both have a cloaking device, and the DNC can be a mean healer while running full aux. Just pop Aux2Batt when getting ready to fire the spinal lance. No other escort beyond a weird Armitage spamming fighters (Fighters are useful in pve but useless in pvp.) or a weird Prometheus spamming science skills (with only just 3 slots...? Really?) can use them properly.
What I'm wondering is how effective would a defiant with them be? How effective would it be to use one pair of them mixxed in with a more standard weapons layout on a defiant, just to eliviate some of the draw on the weapon power settings? Have there been any postings of the actual cannons? has the ship gone live on tribble?
Having an escort with 4 shield emitters and a 1.3 modifier gives close to 30000 a facing do you need hull at that point? It can use cannons has a decent turn rate has has an incredible layout console carries fighter and wont die and it only loses a little hull the shi is op. And know with the cutting beam you can use its sci abilities phasers 360 degrees. Without having to give a single dual heavy.