Which USB Re Clocker

The Innuos ZENith mk2 only digital outputs are ethernet direct and USB 2.0.  I also have a ZENith mk2 and think I will save for the Phoenix.  I have heard so many great things about it.

I used a Mutec MC-3+USB in a former setup. It did improve the subjective sense of imaging and space in the sound. When used with a newer DAC, it did not improve things.

So: my suggestion is to make sure anything you try is refundable if you don't like it. The effects of reclockers, like those of power conditioners, are very much dependent on the system (and perhaps on the listener).

SOtM txUSBultra works great in my system

The Innous is basically a small format computer board with a standard computer motherboard USB output.  That being said, it does have a very excellent linear power supply (which definitely helps!!).

The stock Wyred 4 Sound Recovery "usb reclocker" might help.  I could not guess on how much it would help.  The Wyred 4 Sound device would definitely be better if you get an linear power supply upgrade.  The stock version just has a  wal-wart switching power supply adapter.  There are definitely better USB reclockers.

The Innous Pheonix is likely the absolute best USB reclocker with a high end linear power supply with extensive filtering/regulation and a OCXO (oven controlled) clock.  Whether it's worth $3k to you is another question.  I haven't directly tested these types of devices, but the general consensus is the better USB signal feed results in better sound quality. 

I have always used S/PDIF coax as the better result.  In my system, S/PDIF coax from either an Asus Xonar Essence card or my (discontinued) Digital Musiland S/PDIF card has resulted in better sound quality than the USB output from my computer motherboard.  I even have a reference high quality USB cable.  That being said, the JCAT USB card is on my list of things to try.

The USB reclockers can definitely help things, but in my opinion, they are like a bandaid for a flawed source.  In my opinion, it's always best to have the signal clocked properly from the source instead of "fixing it along the way".  That pretty much means a different music server. 

I have found that the Innous music servers actually are not fully transparent to the audio data.  Even the music servers will alter the waveforms with their DSP logic.  If you like this altered/smoothed sound, then that's great.  It's all about personal preference. 

The USB receiver in your DAC may or may not be high end.  Can you tell us what your DAC is?  Depending on what you say, it could be that a really good USB-to-SPDIF converter might end up being a better choice.  Something such as the Singxer SU-6 with a linear power supply.  If you do DSD, you can still support DSD output through i2s if you have an i2s compatible DAC.