There’s a benchmarking feature you can actually use to test this. If you select Null Output backend in HQPlayer settings, you can run such tests to estimate how much faster computer you need. This backend just throws away the processed data without doing any output. This allows processing to run at full speed. As usual, at the end HQPlayer reports elapsed playback time in statusbar. Comparing this playback time to the content length you get idea of the processing speed vs playback length,
You can try with both Multicore DSP set to auto (grayed) and set to fully enabled (checked). At the moment, only some AMD CPU models seem to perform better with fully enabled (maximum parallelization).
I would say 1024x DSD would be enough so far, since that is IIRC the maximum DACs today support.
sinc-L would be also fairly taxing one, but GPUs greatly help that one. Although for DSD1024 you may be running out of GPU RAM on all models.
Those are all massively parallel computers, they don’t have particularly fast individual cores. Just many of them. But not all algorithms can benefit from such massive parallelism. So for above case it would likely do worse than i9-10900K which is current king of per-core speeds (single thread performance).
Such machines would be however useful for quickly converting your entire music library offline. It could possibly convert several terabytes worth of music library in minutes.
I don’t know, I have to say I have not spared much thoughts on quantum computing so far. It is quite peculiar area of computing on it’s own. Very good for cracking crypto-algorithms or such. Not sure about audio.