Apple Mac Mini (+HagUSB) - exactly the size you are looking for.
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In addition the the Xray, I know of Audionote and possibly Teac/Esoteric.
BTW, a really cool system for WAF is a half size transport connected to a Red Wine Audio Reali-T preamp/DAC/amp (all in one tiny box). The Clari-T amp built into the Reali-T combo requires high efficiency speakers, but it sounds excellent and it is tiny. The reali-T combo box is about the size of a half size CD transport.