Well, 3rd time is clearly the charm:
1. Sony 907 that I used with my MD. Hated it with the iRiver and it was entirely too quiet (even at highest gain setting, it was totally insufficient in anything bigger than a largeish room - entirely unacceptable in a theatre).
2. Tried the SP "high spl" powered mic. The gain was much better, but I didn't like the actual sound quality. Finally (and as somebody else suggested in another thread here back in August (!), Chris at SP talked me into trying...
3. A twinned pair of AT831s. FINALLY! I'm very happy with them. They still clip a bit at the top when I have it set on a "nominal" level and walk away without monitoring, but it's far and away the best sound of the 3 setups I've tried; I'm very happy with them.
Many thanks for taking the time to answer my questions, and special thanks to Chris at SP - what a great resource!!