Yeah but you bought the 650s so we can't really trust what you say!
Actually what you say makes sense if one wants more than one amp.
I always thought a tube DAC and the O2 would be a fun combo or that if I had a tube DAC, I'd want a transparent amp.
I have tube amps but still prefer 'musical' NOS DACs...so what do I know...
DACs are solid state, they use IC's not tubes. Amps can use tubes, or not.