SIIG USB SoundWave Optical 5.1 (maybe PC only?)
Zalman USB ZM-RSSC Optical + Analogue 5.1 output. (maybe PC only?)
Hercules DJ Console - USB, Mac and PC, control surface, Optical + Analogue 5.1 output.
M-Audio Sonica Theater USB 7.1 Optical Output - Mac + PC? BUT: “OS 10.3 required for Dolby Digital and DTS pass-through using Apple DVD Player”
ESI Gigaport AG and Gigaport DG - USB 8ch analog + optical (AG), and ADAT output (DG), Mac + PC, Asio 2.0 compatible.
—-> these look good!!! (although on further investigation, they’re quite old).