As Mofimadness suggested it may be a side step rather than an upgrade to replace the Dr-15's with DR-9's. I'm using the Dr-15's with Apogee Stages and a passive preamp. There appears to be a real synergy happening and I'm very pleased with the sound. I was told earlier that Jason Bloom used the Dr-15's in his development of the Stages though I can't confirm this. I think the Dr-15 was the last amp to contain Dave Reich's signature, alongside Glen Crue's. The speed issue I mentioned earlier has been noticed by other owners of DR amplifiers. I've been told it's a result of using four large capacitors instead of multiple smaller ones that Classe subsequently used.
Classe DR-15 amplifier compared to Classe Dr-9
I have two Classe Dr-15 amplifiers used in bridged mode and was wondering if they compare favourably with the Classe DR-9's. I find the Dr-15's to sound really good, not as fast as today's amps but otherwise very little to complain about. If the DR-15's compare favourably to the Dr-9's I may forget about replacing them. Any input would be appreciated. Thanks.