HiFX are reputable, they aren’t who I work for (SGM-FX). Same sector though.
What level of documentation you need may depend on where you were located then, how much you were transferring etc. But the regulations around money-laundering and Know Your Client are being tightened up all the time, so it might well have changed since then.
Ironically HSBC are one of a number of UK banks to be very heavily fined under US money-laundering legislation!
If you want me to put you in touch with someone at my place, email is in my profile (I don’t get commission so I’m not going to try and sell you it!).
Alternatively, if you used HiFX before then they’ve probably still got you on their client database. So you wouldn’t be starting from scratch, but quite likely they will need to see some of the documentation again as it is probably ‘stale’ by now.
I’m probably at the limits of my competence here, so best you talk to sales staff at whichever company you choose to get the full details :)