Thanks Guys - it's always useful to get a sense of what is going to do the job, and is well proven by real experience. I'd picked up on the EM806 and the AM882 from previous mentions, but hadn't appreciated how they related together, nor into the grander scheme of things. Sounds to me - with an eye to good value - that the AM882 is the way to go.

So, the next question is where do you guys suggest I get them from? Google and Ebay don't seem to throw up any options in the UK, so is it a case of ordering from a trusted supplier in China? Slightly fearful of counterfeit ones, so a reputable source is important here I guess. Either way, any suggestions gratefully received!

Jazz - thanks also for the answers to my voltage and current questions. That makes sense! I recall now that you have to include a bit of margin on voltage for the back EMF, but knowing that 10% is reasonable is a great pointer. Hence 80v drives for my 68v supply seems ideal. Good points also on the current - if the driver limits this, then it is essentially under its control, so less need for much margin. I like it when things all make proper sense!