Is usb reclocking necessary?

I’m running Innuos Zenith MK3 and Ayre QB9 Twenty DAC that sounds pretty darn good. Will adding a Innuos Phoenix reclocker make it MUCH better?
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.

If you have a 10 MHz hook up on your dac it for sure makes it better in every way it fleshes out more in the recordings.

I have the SOtM SMS-200 Ultra Neo as streamer and the Wyred4Sound USB reclocker made the sound worse.

Before trying USB reclocking, I would strongly advice you to get a good DDC (like the Audio-GD DI-20HE), before the DAC, mostly if it has I2S input, no to reclock the USB signal, but to convert it to an easier digital signal for the DAC to shine at it's Best.

Another good improvement is the Uptone Etherregen switch.

Also using a 10 Mhz master clock with everything you can in the digital chain will help considerably. Both, the DI-20HE and Uptone Etherregen accept external master clocking and improve with it.

Also antivibration and AC treatment help A LOT.
You all have obviously been at this for awhile. I’ve been out of it for 40 years and just getting back into it. I don’t know what a 10 MHz hookup is! I did add a Furman power conditioner/surge protector and it made a slight sonic improvement. I have a carpeted floor and putting the floor standing speakers (Volti Razz) on thick pavers improved the bass too. A good step might be to add a good turntable to audibly judge the digital reproduction against. That may tell me where to stop tweaking. Thank you all for your input!!
You know, looking at your question again. The answer is clearly no, the Ayre is an excellent DAC so it is not necessary. You will likely enjoy a good turntable. While my Ayre is a good DAC, it does not approach a good analog end. There are so many great turntables out there… but don’t forget a great Phonostage is required to get the most out of a good turntable. I am just listening to an analog recording and marveling at its wonderful sound.