Pass Labs is An absolutely terrific company to deal with, in terms of answering questions, servicing products and of course offering outstanding equipment. Many companies are good. Pass is among the greats!
I've also had amazing experiences with Bryston and Rogue. Rogue is really exemplary!
These companies treat you with respect and take their time to answer all your questions a true pleasure to work with and they also and most importantly have the knowledge and experience to make the proper recommendations.
There are a few companies i've dealt with that I consider standouts where customer service is concerned... Pass Labs, Atma-sphere, SVS, Placette, Wyred4Sound and VAC are all simply exemplary in this regard.