Why does anybody need a TCXO in a USB DAC? TCXOs are intended to have better temperature stability than ordinary XOs but temperature stability has nothing to do with jitter, which is the more important consideration in DAC design.
The only thing the 12MHz XO is used for is USB communication from the DAC to the PC and none of that communication has anything to do with the accuracy or timing of the sample data received by the DAC. Any two cent XO will do the job.
The 33.8688 MHz TCXO provides asynchronous reclocking of the DAC signals and all asynchronous reclocking does is increase jitter. Again, temperature stability is irrelevant. From the photos it appears 74AC74 flip flops do the reclocking. The 74AC logic family is renowned for signal noise and ground bounce. The chips are cheap because no one uses them for serious products any more and they are a glut in the surplus component market.
The TDA1543 was designed as a 16-bit 'budget DAC' and, as such, many corners were cut. Its THD and SNR specs are more in line with those of a 13-bit DAC. These chips are also cheap and a glut in the surplus component market.
Of course, that's just my superficial technical analysis. The DACs may sound wonderful, but I doubt it. I have one of those acclaimed, 'giant killer' DACs with 8 parallel TDA1543 chips and I know what they sound like.
