*Full disclosure - I purchased my TT 800 through the Mesa artist relations program*
To contribute to the discussion on the TT 800 as a preamp for recording/DI purposes; this is primarily what I am using mine for currently.
I own a Jule Monique, Shift line Olympic, and previously the Noble DI. I don't currently have my Monique as it's currently locked up with my touring setup, and I don't currently have access.
I have been able to A/B it to an Olympic and Noble DI, a number of studio preamps (Neve, API, UA LA-610...etc), Tube DIs (Audio Kitchen & Demeter), and also the DI out of an Ashdown CTM 30.
Long story short - the TT 800 has been in use on the majority of my recording work in the 4 months since it has arrived.
It delivers all I would want/expect from a high end tube preamp, and in particular the brand of overdrive/grit it delivers is more desirable to my ears than the alternatives mentioned above (though the Simone from Jule seems to deliver on this too).
And on top of that I get two flavours of preamp in one box, that is also an amp.
- The Olympic is most similar to the Boogie channel, though lacks some of the dimensionality and depth afforded by the TT800's architecture, as well as having a more limited EQ section compared to the Boogie channel.
- The Monique (and P15 from my understanding) offers something more B15 inspired in voicing, tube and EQ choices.
Not having my Monique to directly compare to, my memory suggests the Subway preamp EQ is more similar to that voicing, but with a variable mid control and hi-pass.
- The Noble IME is not what I'd consider particularly amp-like, and shares more in common with the UA LA-610 preamp in it's sound (to my ears), providing a big warm, creamy, tube-y studio preamp sort of sound. The TT800 can do something similar to this in the subway channel, but I find it to exhibit more harmonic excitement which gives a different presentation to the upper mids in particular, and more of that tube amp "bloom" and dynamic interaction.
- The Ashdown CTM30 shares a similar EQ in some ways to the Boogie channel, but is a very different voicing, and has a higher degree of interactivity between it's EQ controls, as well as much more distortion and dirt available.
The Pre-EQ out of the TT800 is great, and sounds wonderful with any combination of the deep and bright switches, and even with both active it's never too mid-scooped for my needs, and in flat settings compares favourably with the other options available to me. Without any voicing switches engaged all three offer nuanced voicing differences on similarly quality sounding tube-DI sound.
The other thing I have explored has been to take the FX send out of one channel (generally the boogie channel) and use that to feed a separate DI (RNDI or Lightning Boy TI box), whilst then having the other channel active on the amp and feeding a speaker. This then frees me up to EQ one channel as I'd like for a straight DI'd tone, and the other channel can be EQ'd for the speaker cab/mic setup.
Ultimately a lot of this will come do people's tastes in preamps, and the features, controls, and voicing/sounds they want contained within such a device.
Re: the quality comparison of the TT 800 vs the hi-end/'boutique' alternatives - the TT-800 is, for all intents and purposes, houses a high end preamp with a high end class D power amp, and has all the features and performance I would expect from such an instrument.
I have previously owned a Walkabout, but at the time never used it in this context, and have had no direct interaction with the WD 800 outside of trying it in a music setting, so can offer no meaningful comparison there.
Hopefully some of this proves to be of some help and interest to some here.