It's the continuing desktop clusterfuck. Like an arse, I decided to add an analogue source as well, so I needed a preamp. Thought I'd run it active with the headphone amp on the tape out and the powered monitors on the pre out. But it turns out there's a wicked hum in the speakers that way.
Passive, though, it's beautifully quiet and transparent -- so the bodge setup right now is both sources into the pre, line out to the headamp and loop through that to the speakers. This appears to work fine from a SQ perspective, but still begs the original question about where to be setting the levels.
The simple answer, I guess, would be to sell the lot and buy a Zana and be done.