Huge fan of Dave Hill, the guy is a genius; that being said:
1) While I am really not a fan of Music Tribe, I would doubt there is much of a discernible difference in DAC quality between the M32 and the Hedd Quantum, especially on most PA's. In my experience when I have grabbed tracks from my live work and brought them back to a high-end monitoring setup, the console DAC/preamp on the front end has not been noticeable; I can sure hear the player, the instrument, the mic used, the mic position, and the acoustical space though! Between A&H QU Preamps and DiGiCo's 32-Bit Stadius preamps, I haven't noticed a difference when working on tracks! We recently got some Neve preamps at work. We double patched the channels to the DiGiCo and the Neve, once we gain matched them, we couldn't pick out which was which, either on D&B PA or Amphion monitoring rig setup for broadcast. We sent them back.
2) Dave Hills products are not usually inexpensive; is this the best ROI for your rig and system? If you are looking at a DAC might I be guessing you don't have a digital DSP for array processing? If so that can offer many noticeable advantages, especially if you have 1:1 box resolution (frequency shading, low-mid beam steering, subwoofer arrays etc); the Meyer Sound Galileo Galaxy is the most flexible one I have found, and I am starting to see it go out with non-Meyer rigs (looking at you L'Acoustics!).
3) If some distortion or "warmth" is what you are after, perhaps a Waves rig might be a good investment? It would add a lot of useful tools such as having dynamic EQ and Dessers available on each channel, (I have found the X32/M32 Desser doesn't do too much); both the NLS and Scheps Omni Channel plugs offer some nice saturation options. Personally for mixing live, I often prefer saturation to be on the source or group side, rather than the outputs. On some sources or groups it gives things the tonality I am after, but rarely do I want that across the whole mix (talking heads? Video playback? iTunes? etc etc etc), unless it is extremely subtle;
but if it is extremely subtle it probably is not the best use of funds.
4) Depending on how your PA is driven this could cause issues. Many setups for example send L, R, FF, and Sub. If you put this device across the L/R you will have introduced a timing/phase problem, and now you would have tonal variance between FF vs mains, additionally you have probably moved the acoustic crossover frequency between your subs and mains. I would strongly recommend against all of that.
Things being in phase and how the systems-engineer tuned and intended it to work, almost always sounds far better than the addition of any plugin or piece of hardware. If your system DSP breaks out from L/R to your various sub systems than this could work, but if it doesn't you will be causing a headache for yourself, any visiting BE's, and whoever takes over down the road. If in doubt, you can use SMAART to create a transfer function between your PA L/Sub send, and real-time this can let you know if you have latency problem!
----
Bottom line: I feel like you could probably spend the money elsewhere on something that would make a bigger difference to your audience. Invest in some nicer mics, higher end DI's etc. I like to put my purchases through the lens of:
1: Will it make a difference to the audience and player experience
or just me?
2: When I have moved onto another gig, is someone reasonable going to love what I got? Or will they question my sanity?
I have been on both sides of that equation, I have come into some cool tools and well designed/creative setups, and learned new things from them; other times I have been royally pissed at what someone before me spent money on!
At the end of the day, there are some tools that I simply enjoy using, so I own them personally and bring them out when I want to. Not all gigs provide Neumanns, so I try to make sure I have some on me!
----
Also I know you probably already no most of this, I am just covering the bases!
---
Out of curiosity I would love to know more about your venue and rig?