Is usb reclocking necessary?

No

With Asynchronous DAC like Ayre QB9 data is not delivered in real time*. Asynchronous means that USB clock and DAC’s D/A conversion clock are independent (asynchronous). Reclocking Asynchronous USB doesn’t make any sense. On the other hand "Reclocker" might have built-in filters on data and power lines that reduce injection of digital noise into DAC (always good thing). I would search for USB filter (but such filter might be already built into DAC).

*Computer sends data in "Frames". Each frame contains multiple music samples. These frames come at slower rate - likely 1kHz.
DAC places them in the data buffer signaling back buffer’s under or overflow. Upon this signal computer adjusts size of next frame.
That way clocks are independent, but data is not lost.

I think the Ayre's USB interface is powered by the DAC power supply so it doesn't draw anything from the computer. A filter for the power lines would be useless.

When DAC is self powered, then USB power is not necessary but GND connection is still required since single ended (GND referenced) signaling is used at the start.  It might be possible to lift the GND after music started playing as long as data common mode stays within input range.

That depends. Re-clocking reduces jitter. If you have a sufficiently good DAC ($$$ is not always good or sophisticated), the jitter is already handled - maybe better than the re-clocker. I did see some test data that indicates that many reclockers are not all that good.

However, jitter makes a big difference. Since I am beginning the process of DAC design, i started by adding USB interfaces to two old, but excellent in the day, DACs that were S/P DIF only (one step ahead of smoke signals).

Holy smoke signals batman! What an improvement. OK, OK, low bar, yea, but it goes to show the fundamental issue we’re dealing with.


Now if you reclocker is <<< than your mega-bucks DAC, it ought to, uh, worsen jitter.
Its neither magic nor rocket science. Its jitter, which is the X-axis in the Cartesian system that translates a digital code to an analog waveform.