Jackd,
Yes, I initially did suspect the output of the modded Sony, however with the adapters it works fine on a single-ended connection to the Nuforce preamp. Obviously there must be input circuitry differences between the DAC-10H and the Nuforce pre.
Ultimately my wish would be that the 10H had a set of balanced input connections as does the Nuforce MCP-18 (which really is a very nice unit when used as a transparent volume control - it will replace my Wyred-4-Sound STP-SE).
The ST-10 is quite good with the MCP-18 but the differences between it and my ncore NC400 are subtle. The build quality/fit and finish of the Nuprime pieces are impressive.