So I have used my Mixpre-6 for 8 shows so far. While I like it quite a bit in general, I would have to also say I've had a lot of issues also...
... I found using advanced mode instead works out much better....
Thanks for the feedback. I guess I can add some of mine too. I've recorded using the MP6 for 4 shows now. I will say, I've used advanced mode, and it seems like that is much more straight forward and has less hiccups.
I guess I should be test to be positive, but I'm pretty sure my previous settings are saved between power cycles (in advanced mode anyway). Definitely saved between power cycles, not sure if they haven't even been saved when no power is available (4AA pack taken off briefly to access SD card, no USB power).
I have set up profiles: one profile for 4 mics in all requiring phantom, one profile for 2ch mic recording with phantom, one profile for 4ch recording using 2 mics with phantom and 2 channels line in without phantom (all using XLR inputs). I haven't set up a profile yet that includes channels 5-6 on the aux input. Regarding configuration saving between power cycles, I've done on the fly adjustments to the profiles to change the gain levels compared to the saved profile, and the changed gain setting has been saved after power cycles.
You can set up the * key on the front for different functions. I have mine set up to access the menus for Channels 5 and 6. This makes it much quicker and easier to arm and use channels 5-6, much more like the menu availability for Channels 1-4.
Other than the first outing, I have been using a 20,000mah USB-C battery and using a USB-C to USB-C cable for the power connection. (Mine is a Jackery USB battery, which seems like a lower cost ripoff of the Anker USB-C battery.) Powering with the USB-C battery has worked without problem, avoids the use of the bulky Sound Devices USB-A Y-cable, and still allows for the backup powering by the 4AA battery pack, though I've never bumped over to it as far as I can tell.
I will say, the Advanced mode has worked great for me. As much difficulty people are having wrapping themselves around the Custom mode with Basic gain, I'd encourage more people to try it. First time out without any experience I dialed in 18db of gain for one set of mics and 22db of gain for the other less sensitive pair. My peak ISO levels for the 4 shows I've done across the 4 channels has been in the range of -14dbFS to -12dbFS. I've just kept the fader levels at 0db gain (noon on the dial) for the LR mix track, which I've just ignored anyway. Post-processing to add back (normalize) 12-14db of gain and it sounds great.
I'm sure I can dial back the gain beforehand for very loud expected shows (like on stage taping) and add in gain for amplified acoustic music and still guestimate to get myself into the -20db to -10db range. Limiters are on just in case, but setting up the gain beforehand in Advanced mode, being conservative, and boosting a bit in post works great. If I were to put it into custom mode with basic gain, I'd probably find myself needlessly riding my levels using the gain knob, and it would just sound worse due to all the level changes I'd have to endure during playback.