I own a SD Mixpre6, and believe that it is superior to the 744 for
my needs, for the following reasons:
1. Price.
A new Mixpre6 sells for less than a used 744.
2. Inputs.
Whereas the 744 has only 2 mixc pres on xlr, the mixpre6 has 4.
Whereas the 744 has 4 total channels (2 x Mic/line, 2 x line only) the mixpre6 has 6 (4 x Mic/line, 2 x line only). Those extra inputs are really helpful. Even if you don't have a 3rd pair or microphones, you can use that extra pair for a SBD patch or a line out of another Taper's gear.
3. Powering options.
The Mixpre can be run from a large capacity usb-c battery, internal AA batteries, & sony L type, whereas the 744 has only a hirose and L type. The bug usb-c battery runs the mixpre6 for over 18 hours and is smaller and lighter than any of the hirose solutions. A RA>RA USB-C cable makes the thing sit in the bag so well and is secure enough that I no longer run any kind of backup.
4. Size.
The Mixpre is
much smaller than the 744. It's smaller than most small preamps tapers use, this means it fits in a much wider variety of bags, and is even
friendly in a way a 744 isn't.
5. Wingman app
When I clamp- I love setting up my rig, closing the bag, dancing a few feet away, and starting and stopping (and monitoring levels of) the recording on my phone.
The only reason feature the 744 has over the Mixpre6 is its digital input. But If you're running an external AD converter and using the 744 as a bit bucket, you're not using any of the other fancy features of the 744.
The specs on the Mixpre6 are "better" than those of the 744, but I don't believe that you'd be able to hear the difference in a real world scenario.