i had forgotten about this thread. Sorry I never responded back to my own original post once I got further in my own search.
In the end I tried a number of different solutions. Adapters seemed to be less than ideal for me on a number of different single-ended amps, including the Atma amps I had that also had single ended inputs. I tried a few different pairs from some decent brands. Balanced out and in from the Atma gear were great. All the adapters, if I recall, seemed to collapse the sound stage and ultimately seemed to be a poor solution for the quality of the rest of the gear, including the MP-1. There was also a bit of noise that was inconsistent with the amps fed from other (unbalanced) pre-amps I owned.
I sent the MP-1 in for service (for a different reason) and while there I had Ralph install some single-ended outputs which included a switch. I will admit when I got it back I didn't totally understand what the switch did because in either position there was the same level single-ended output (it also didn't appear to cut off the balanced output). I didn't have the greatest luck with single-ended connections out of these outputs either, again with a pretty large number of amps I tried, and with the switch in either position. Similar issues, but maybe even more noise than with the adapters, or at least as much. I remember being pretty dissatisfied overall. Impedance issues between the pre and the amps? I don't know, but that's what my un-educated brain concluded.
Later settling on some fairly high-end SET amps, I got a bit desperate and through research took a long-stretch last chance on an Art Accessories Clean Box Pro. This was WAY outside of what I was going for but somewhere I had read that they were very effective even in some pretty serious systems, wall wart powered and all. In an ultimate irony I had $1K balanced cables going to $1K RCA cables with a $79 converter box sandwiched in the middle. Ironically enough, the whole setup sounded pretty amazing, low noise and much better sounding than I had reached with the MP-1 and these unbalanced amps, and I ran with that configuration for probably 18 months.
In the end I bailed on the Atma- pre-amp once I had found another that worked better for me, knowing I wasn't going back to balanced amps again.
Worth a $79 try if you're in the boat I was in...just return it if it doesn't work.
