I am currently Rear Admiral, Lower Half (42), and for the last 13 levels have been stopped by this one particular mission. I cannot seem to beat the Romulan ship Sithesh, from the Romulan front mission Ground Zeros. It's heavy photon torpedoes keep tearing me to shreds.
That is a though ship to beat(no matter what difficulty level you are playing). It took me quite a few runs..and a bit of luck.
You could always ask someone to team up with you for the mission, if you do not mind help that is
Advanced Escort Prometheus model (U.S.S. Serenity Valley)
- (very rare) Plasma Beam Array Mk X [Acc][Dmg]X2
- (very rare) Transphasic Torpedo Launcher Mk X [CrtH]X2 [Dmg]
- (very rare) Plasma Turret Mk X [Dmg]x3
- (very rare) Tetryon Dual Cannon Mk X [Acc][CrtH]
- (very rare) Plasma Beam Array Mk X [Acc][CrtD]x2
- (very rare) Quantum Mine Launcher Mk X [CrtD][CrtH][Dmg]
- (very rare) Disruptor Turret Mk X [Acc][Dmg]x2
Looking at your weapons, it does seem to me that you are mixing quite a lot of different energy types.
You have plasma, tetryon and disruptor. It would be wise to choose one of them and stick to it, because having different types will eat your weapons power..and makes it difficult to support them with consoles, too.
You seem to have lot of plasma already, so maybe you should replace the disruptor turret with a beam emitter( or something like that.)