problem resolved, i think.
new sof firmware update came out, not sure its arrival was more than a coincidence
1 - disabling all intel vitrualisation options in the helix bios was enough to allow the fw to load thus pavucontrol was now seeing input bars moving but no sound output.
2 - ran alsactl -U init after i noticed ucm errors when running alsactl init.
3 - aplay -l now sees all 3 cards when docked and 2 when tablet only.
4 - alsamixer still showed the correct hw but a lot of outputs were muted, by enabling and disabling them all in sequence enabling the front dac enabled sount from the rt256 card and headphone socket.
I'm doing basic checks like detaching and reattaching to see if that affects the sound, so far ok Only noticeable thing is the fw gets reloaded 3 or 4 times a session, but doesn't seem to affect anything . If i have not commented more in a week feel free to close the bug.