I should step in here, because I am using an Aesthetix Io (Signature, one power supply) with a Bent Audio NOH (TX-102) passive pre right now.
I've found that with my .2mV output cartridge, I need to run the Io at its top gain setting, a whopping 80 dB, to achieve good dynamics with the NOH in my system. This might not be such an issue with higher-output cartridges.
I should mention that the amp is an Aleph 3 driving VMPS 626Rs.
John Chapman of Bent has been very helpful in troubleshooting this situation. The impedance matches should all be fine (Io output impedance is 300 ohms, Aleph input impedance is 10Kohms).
At this point, I have several options:
1. Add volume controls to the Io and dispense with another pre. I'm sure this would sound the best, but would cost me $3600, which I'm really trying to avoid!
2. Change up my amp. Maybe more headroom would help the dynamics. When I had the Io at 72 dB gain (which theoretically should be fine, delivering over 500 mV at the power amp input), I had to run the Bent passive unit with the volume almost all the way up - which doesn't make for the best performance according to John. So maybe my system is really asking for a more powerful power amp. I've considered Ampzilla 2000s, Son of Ampzilla, the Mcintosh MC402, the MC501 monos and (since I'd really like to stay Class A if possible) the Forte 4A and the Threshold 200.... just not sure if those two give me the extra headroom and oomph I need.
3. Just go back to running the Io directly into the Aleph, no volume control. Incredibly inconvenient... and incredible sound!
Bottom line: putting something between your phono stage and your power amp is always going to detract from the sound. So far, the Bent Audio is peforming the job OK for me, but I'm still missing the clarity, soundstage, presence and dynamics of NOTHING.
Patrick