If your recording device takes optical input, just get a digital format converter and run out of the coax output. I've used and like the Hosa ODL-276 S/PDIF coax <--> S/PDIF optical converter. Cost about $60 shipped from Full Compass (call, do not order online). No point in spending $450 on a Microtrack + CF card v. the $60 for a DFC, IMO - unless you want to make the jump to 24-bit, anyway.
Are you -positive- the problem lies with the UA5's optical output, and not a cable, or your recording device's input?