I second what Levi said about Richard Gray products. I have 2 of the 400s and couldn't be more satisfied as to what they have done for my system. Check them out. You won't be sorry.
I was just looking at their stuff, and evidently isolation transformers are evil and you should use their "parallel" power conditioner.
Oh, unless the isolation transformer is a Pole Pig or SubStation, then it's good.
Judging by the price of the Pole Pig, their products are more expensive than some competitors. Maybe you're paying for the fancy case.
I'm also a bit puzzled by their practice of using an MOV to protect your equipment, then using a fuse to protect the MOV. MOVs don't last forever, they are degraded by each surge that hits them. In other words, they're disposable.