i got a cheap, generic 6 pin fw card and a 6 pin cable and now it works perfectly.
i think the problem was caused by using a heavy duty 'pro' fw cable. this was too heavy for the little 4 pin socket, which is soldered directly to the mother board.
as far as other problems go:
the mixer app is buggy; somerimes the meters stop working, the 'soft' volume knob hardly ever works and the gui gets sluggish or locks up completely.
any buffer size bellow 512 is not usable with live for more than a few minutes before the sound starts to break up in horrible ways.
it's ok if you don't care about latency.
all i have to compare it to is the terrarec pci card in my desktop pc, this sounds noticably better than the 410 and works reliably with a buffer size of 64.
i desperately need better performance at low latency, but there seem to be no guarantees, and i can't afford to punt another £300+ on the off-chance