Whirlwind ISOXL Line-Level Isolation Transformer, 3-Pin XLR Male/Female Connectors at Amazon

Jesse at Pine tree makes a balanced to unbalanced converter. It is an amazing piece. I use it between my Lumin D2 and amplifier. 

Ground loop.
Power amp should have grounded AC.
Lift ground to the preamp.

Use only unbalanced RCA interconnects.
Unshielded twisted pair is best, by far.
Unless the system is balanced in and out, there is no advantage to a balance XLR cable. No need for a transformer or other performance robbing accessory.

K.I.S.S..

I have a device with dual jensen transformers—the expensive ones—works for hum, but really takes the slam out of drum hits and the like. Using a crown drivecore amp with balanced inputs—lots o slam! If one cant find the nice xfmr, jensen has a website last time I looked. That gadget that costs $450–those are the good xfmrs, but the cost might go towards an amp change. I like the balanced to run a 30 foot cable—zero noise of any kind.