TacT, Altmann DAC not connecting

Big frustration - I got an Altmann DAC to take the 192 khz output from my TacT 2.2XP. At louder volumes the sound is fantastic. I love the Altmann - with room correction, SET vibrance, and 20 hz extension, the icing now has a cherry on top. There's always a "but".

At quieter volumes, the thing is noisy. It's related to the digital volume control/output level - it makes the same noise run direct out of my battery-powered squeezebox when I use the digital volume control.

I've gone around for a few days with Charles racking his brain. He's been very helpful but we have not identified the cause.

1) Both the TacT and Squeezebox have 24-bit outputs, while the Altmann is 16 bits
2) The noise is the same with Toslink or RCA
3) It sounds great with the volume level up, except for quiet passages of songs
4) I'm using a different 12 volt battery than Charles has used, though he says this is irrelevant.
5) TacT says the 2.2XP is compatible with 16-bit outboard DACs
6) I have used an Ack! 2.0 and battery powered Monica-2 on this systejm, both 16-bit, with no noise issues
7) Charles' thought is the 24-bit signal is being truncated somehow
The noise is worst with 192 khz out of the TacT and "best" with 44.1, but also is present with 48 and 96.
9) I managed to get an .mp3 recording of the noise and can attach that file, but I don't see anywhere to do that here.

I'm really stumped. Smart digital people, please help.
Upon further review, the Squeezebox is not nearly as noisy as the TacT.
Update - I tried an Ack! 2.0 in the system yesterday. It had the same noise issues. I used to own one and it was quiet, I think it must have been before I upgraded from the 2.2X to XP.
The TacT has been sent back to TacT. We'll see . . .
I don't know what to tell you. I have a very similar system (Squeezebox, TACT RCS 2.0S, Attraction, BYOB amp, Sonus Faber Cremonas) and have not heard any noise issues at all.

I did listen carefully to the TACT putting out 44.1 versus 192 into the Attraction DAC and thought that 44.1 sounded slightly better.

I should probably also mention that I'm not currently using the TACT since the Cremonas are fairly flat in my room.