the general rule is 10X output impedance of preamp is the minimum acceptable input impedance of the amp. Ref6 600 X 10 = 6k. The Rowland input impedance is 40k, so should not be any issue. There are very few amps it would not work fine with. I have a ref6 also, great preamp!
Audio Research Ref 6 work with Jeff Rowland 725
I just bought ARC Ref 6, it sound excellent and I love it so much. I want to know if anybody know how does it work with Jeff Rowland 725 Mono-block amp? Does it sound good? I'm planning to buy a new amp to replace my 5 years old Electrocompaniet AW-180 amp. I don't want tube amp, just SS amp. thx.