Nah, I never resolved it, the pic still looks soft in HD - and in the intervening months I've changed my TV and AV amp.
I'm loathe/lazy to reflash from scratch especially as I hear there are some probs with the latest openvix.
I have all 4 tuners working, I have the 2 hybrids side by side at the back left edge (A and B) and then the 2 sats together nearer the middle (C and D) and it all works fine (except I still have this annoying boot from deep standby to record and the unit will just remain on, NOT go back to normal standby while recording, meaning it won't return to deep standby when recording is finished - I have all my updates for channels/guide etc set for 4 in the morning so it shouldn't be that - ho hum, maybe I'll get round to flashing it at some point..)
Hope that helps.