DanO, and a couple of others have asked about setting the mic an vocal harmonizer on the Audya. Not saying it is right or wrong, but here is what I have settled on.
Main Mic:
Level: 63
Compressor: Either Off or -18db 2:1
Limiter: Off
E.Q.: 8 kHz +4 db
5 kHz +2 db
3 kHz +1 db
1.9 kHz 0
1.1 kHz -1 db
All other frequencies: 0
Vibrato: Off
Pitch Correction: Off
Reverb: Church Reverb Mic Level: 50 (adjust under Menu, DSP, Reverb)
Echo: User 1 consisting of these settings:
Mono Echo 1 (adjust under Menu, DSP, Echo/Delay)
Algo: 1 Level: 4 Time: 5
Feedback: 15 HPF: 7

Vocal Harmonizer settings:
I generally use Duet, Country Up with these modifications:
Volumes on 50, Pan to middle
Equalizer: Low Cut, with these settings: 430 Hz: -1db, 265 Hz: -3db, 160 Hz: -7 db, 100 Hz: -14 db (this takes muddiness out of harmony voice)
Vocal Harmonizer Effects settings:
Effects Send: 15
Reverb Preset: Church
Echo Preset: User 1 (same as for main)
Lead: Off (This is important, unless you want the lead doubled.)

When necessary I have used some of the other VH presets with good results without additional editing.
I have used these settings on Sennheiser 855 and AKG D5.
Hope this helps!!

Do your settings allow you to go directly into the Compacts sans mixer, T1 etc. Most complaints are that the Compact lacks mids, can you compensate for that with the keyboard settings?

What are the display dimensions in inches (not resolution)?

I use a mixer most of the time, but not because I'm missing any mids. Sometimes I have another person or two work with me, and sometimes I use my Roland E50 for small, quick jobs and on those occasions I need a mixer. I just leave it permanently in my setup.

I have the Bass boosted just a little on the Audya internal e.q., but the mixer is run flat.

I have heard of only one or two people talk about missing mids, and none of them are Bose owners as far as I know. I just don't hear anything missing.

I wouldn't be surprised if some people are using the old "V" e.q. curve that was necessary or at least desirable with the older sound gear. In that case they are boosting the lows and highs, and in effect lowering the volume of the mids.

At any rate, the e.q. is easily set and saved on the Audya. If you want more mids, just turn 'em up!

To answer your basic question, the mixer is certainly not necessary for me at all 90 percent of the time, when I play alone.

I could also use the second mic input and line input for a duo as well.

But I like to have the mixer along JUST IN CASE the Audya crashes. I could use my laptop for midi files and run it and the mics through the mixer and make it through the job if needed.