hi,
you have to recap the SMD caps on the motherboard. Eventually, without recapping, your 840av will struggle to power up despite the power supply being fine.
They appear to sell more in the States because the guy who bought seems to be a trader and has listed another for 750 GBP.
I do miss the 840av but it would not do 24 bit mode addressing like my Quadra 700.
The on-board sound is terrific, it is the sound of the speech synthesis used on Radiohead Fitter, Happier...
There are some DSP specific apps and i attach them here. This was when having a DSP chip on board was all the rage, think of the Next Cube and IBM's M-wave.