I guess Eiffel is right, here's the correct path to get the original Burson drivers from:
https://www.bursonaudio.com/downloads/.
Sorry if I didn't make myself clear. I did use the Burson drivers from their webpage and I did use the win7 drivers for the three win 7 machines (2 laptops and a desktop) that I tried, unsucessfully to get the DAC to work on, and I did use the win 10 drivers to get very partial success on the win 10 machine. It was just that the first laptop used Windows7 to automatically install drivers for the DAC as I wasn't aware of the need for Burson drivers to be pre-installed - no paper manual and my desire to listen to it overcame common sense. Anyway I uninstalled those drivers and went with the correct versions.
The dac/amp does sound great on my son's Alienware desktop in Win10 BTW, which makes this more frustrating.
So far I have proved that the DAC works on Win10 with JRiver (with the ASIO driver only not what I have read elsewhere is the correct driver, the WASAPI one!). Is my information correct on this, the correct driver to use is the XMOS-XS1-U8 MFA? Not the USB Audio Device?? Others have suggested disabling the USB Audio Drivers and I've tried that but with no success for the WASAPI drivers in either Foobar or JRiver.
The DAC doesn't work with Foobar2000 at all - (i) get an error message when I try to use the WASAPI output to the DAC:."Unrecoverable playback error: Unknown error code (0x88890008)" and (ii) when I switch to USB Audio Drivers I see that there is output in (i) foobar, (ii) in the Windows "playback" popup and in (iii) the control panel "settings" popup, just nothing on any headphones from the jack when selecting the the ASIO driver throughout I hear nothing from the headphone jack at all - switching phones and taking the settings back to the internal sound card proves that there is an output at all stages, I'm just not hearing anything!
JRiver works, as I say with USB Audio Device, but not with XMOS-XS1-U8 MFA, I get an error and suggestion to use the DSP studio to correct the problem (see screenshot). I don't use JRiver so not sure how to tweak that. I don't own JRiver so don't want to have to spend more on this!
If I can't sort this I'll try to get some support from Burson and deal with it that way. Thanks for your help so far.