DC from my Classe DR6 preamp? Solutions?

I have a perplexing problem. I am running a Classe DR6 into a Classe CA150. When at relatively low volumes, things sound OK. At crescendoes or higher volumes, the woofers move slowly or stop and then the power amp's protection circuitry goes on.

With a old NAD receiver with a preamp out, the power amp plays normally.

I just sent the preamp back to Classe for servicing. They said everything ran OK(They supposedly included listening tests) and have just sent it back(They were nice enough just to charge shipping).

Anybody have any idea what the problem could be?

Or are there any suggestions on an independent repair shop in the USA that could help me (Although, they are gracious. Sending the unit back to Classe is a nuisance with customs etc.)?
It is important to know what speakers you are using? I had a similar problem. I found out that the problem was with the surrounds on one of my woofers'. I replaced the cone and no more problem. The woofer was behaving just in the same way, sucking in and than stopping. And by the way I was using at the time a DR-6 and Defy 7 amp.
I am using Totem Hawks. Both woofers are exhibiting this behavior. I just played a historical recording with little dynamic range (Django Reinhardt). There was no difficulty at all.

This problem just surfaced after using this combination for 5 months without this difficulty.
There are probably trim pots inside the DR that will allow you to adjust the DC offset. Yes, I know the factory gave it a clean bill of health, but do yourself a favor. Get a meter and check to see if there is any DC in the output. If so, adjust the trim pot to read zero.