Duet to Touch for next upgrade?

Hmm, not sure that I would look to a Touch as a significant sound upgrade if I already had a Duet + a good external DAC.

The reason I think this is that with the same external DACs, I did not notice a significant sound change at all moving to Touch from Roku Soundbridge, which I would expect to be a bigger change. The move to the touch was justified from both a performance and reliability and usability perspective in that the Roku SOundbridge was an older device that was no longer actively supported or sold. I never have had an issue with sound quality of either ROku or Touch running through the same DAC and system.

What are your goals in making a change? Knowing what kind of sound you are shooting for would help.

Pre-amp generally has a huge effect on sound so trying different ones is a good place to look for sound improvements in the areas of tonality, noise levels, detail/resolution, imaging, soundstage, overall musicality, smoothness, etc.

Also note that SB Touch (and I suspect Duet as well) has volume control onboard so pre-amp is not needed for that. Squeezebox with volume control could be used directly as the source into a power amp accordingly then I believe assuming that is your only source (source switching is the other prime function of a pre-amp in addition to volume control) or power amp has multiple phono level inputs as is sometime the case.

If I already had Duet and looking to upgrade I would get the DAC right first then move up to latest and greatest player device.

Touch is about due for a successor soon I would think and I would expect that to up the ante still at this stage.