If you're okay with spending on cables (and if you have GR then it seems that you are), I'd try and get my hands on some alternative cables. Don't ignore those power cords, either. I've had spectacular luck with Clarity Cables. Best freakin' bass I ever got out of my Merlins when hooked up to my big Plinius amp. Wow. And yes, the mids and treble were maintained -- and in comparison to the Cardas, even extended.
As for Pass, I'd go for an integrated. Class A is very fun, but will "push" more in the mids than a Class A/B will.
You could also try a Luxman. The ~$4k L-505u is a startlingly good integrated (see the reviews) and the $10k L-509u is one of the best amps I've ever heard, period. The Class A versions you might find a bit syrupy.
As for Pass, I'd go for an integrated. Class A is very fun, but will "push" more in the mids than a Class A/B will.
You could also try a Luxman. The ~$4k L-505u is a startlingly good integrated (see the reviews) and the $10k L-509u is one of the best amps I've ever heard, period. The Class A versions you might find a bit syrupy.