Strophoid, I thought you said your friend’s keyboard has USB in your 1st post? Then you say it does not? Did I misread it 
I bought one of those cheap USB to standard midi thingy’s about a year ago +…I actually have never tried it.
I think it’s designed to go from a regular midi out, into a computers USB…if it works the other way around at all (?), it would obviously have to go into a midi router 1st…
BTW, I use Motu MTP AV’s… I have both serial & USB versions…but I connecte even the USB versions from it’s regular midi ports to my sound cards regular midi I/O ports, which works fine & very reliably…unlike USB, where I get tired of issues not being recognized, losing connection, can’t seeing connection 