It looks like the Model S USB release and its specifications came as a surprise in some circles. The major concern is apparently associated with the TDA1541A chip, so I believe I will do well if I address some of these issues publicly.
The first one is associated with the Model S USB 192 kHz compatibility. So, yes, the Model S USB uses TDA1541A and it is up to 192 kHz compatible device. It means that it does not downsample, neither inside the DAC nor on the PC side, but it just converts any 44.1/48/88.2/96/176.4/192 kHz file directly, at its native frequency. Yes, TDA1541A word clock (latch enable) input can normally handle any frequency up to 200 kHz (please see its datasheet, page 6). It should be however also noticed that its bit clock input is limited to 6.4 MHz, and with today’s usual 64-bit frame this can limit usable Fs bandwidth to (practically) 96 kHz – but again, this is not the case with the Model S USB.
The Model S USB doesn’t perform any additional data conversions internally, as USB to S/PDIF – it just decodes the USB and sends it as a raw PCM via digital isolators to the DAC portion of the unit. This ‘raw PCM’ is however not an I2S either, unless you mean ‘I2S’ as a general family name not only for actual I2S specified by Philips, but also for any serial PCM audio format that also encompasses EIAJ/LSBJ and similar protocols, such as Philips’ simultaneous data, used in the old Philips CD players, and now, 25+ years later, also in the Model S USB.