Hi all.
After weighing up my needs, I ended up with the M-Audio Fast Track Ultra. The first unit failed on day two (it went into a motor-boating state and cheerfully remained there ), but the current unit appears stable. I find the non-log nature (or is it non-linear?) of the pre-amp pots pretty weird but all-in-all, it's good bang for the buck.
Many thanks for all your help.
FS
(P.S. Actually I had a another real doozie with the 2nd unit. I kept randomly loosing use of the 2nd headphone jack and all but inputs one and two. Turned out after much head scratching to be the plug blades on the (New Zealand-style) wall wart making only intermittent contact with the cheap power multi box and hence dropping the unit into USB-powered state).