I didn't mean to belittle or offend you in any way, I was just wondering how you're going to figure this all out remotely. MC is quite right, you should just try it.
I don't have a UCX II. Unfortunately, the circuit doesn't seem to be built exactly like the UFX II either. At least as far as the adjustment range of the gain from the Instr input is concerned. So, a description of my setup will probably not help you much. But if I understand you correctly, you wanted to know (I have also kind of "low volume" pickups (Gibson 59 Classic)).
So, let's go.
I can only record quietly at home and use a few tricks to get a nice creamy lead sound despite low volume.
Current setup: https://www.tonstudio-forum.de/attachme … -2022-jpg/
I plug the guitars directly into the instrument input of the UFX+. The gain can be adjusted from 8 - 50dB. For humbucker guitars I use 20dB gain (Inst 9), for single coil guitars 22dB gain (Inst 10).
All humbucker guitars have the Gibson 59 Classic installed. On the Tele Texas Special. The pickups are adjusted from the string spacing so that the strings can vibrate well. The adjustable pole pieces on the Humbuckers are set so that the strings are not different loudness.
I record the direct guitar signal to be able to use a VSTi or reamp afterwards if necessary. Usually, the signal is sent to an overdrive / tube amp and are miked with two Mics (SM57 and Tube Mic).
I often use the UFX+ as a tape deck via DURec. The recorded signal from an L5-CES at the Instr input sounds pretty decent even as it is.
In this setup, the UFX+ acts, among other things, as a parallel effect loop for the two Marshall combos (stereo setup). I send the preamp signal directly back to Effect Return. The times for the A/D and D/A conversion are pleasantly low. This gives me a lot of the dynamics of the preamp signal.
The UFX+ also connects the two Lexicon PCM 81 and PCM 91 as external FX. I can then mix them in 100% wet in the direction of the effect return (of both amps). By appropriate routing, I can use the PCMs either for guitar or DAW as FX.
Via TM FX Snapshots and the ARC USB, I can choose between the two Lexicon FX as well as between 4 different FX levels to bring either the guitar or the FX sound more to the fore.
The UFX+ also sends the guitar signal from the instrument input to a Rockboard rack tuner. With the Roland FC-300 I can tap in the tap tempo and send it to both FX via MIDI. With the two FC-300 pedals I can also control the "adjust" parameter of the Lexicon FX via foot pedal and other parameters of my choice (decay, reverb intensity, etc.).
The UFX+ Instr inputs work extremely well. If that wouldn't work, I would bring the output of the guitars to line level.
Sound examples:
1. Guitar Overdub (using Les Paul, guitar on right channel) - backing track and amp recorded with DURec, later mixed in Cubase
https://www.tonstudio-forum.de/attachme … orrow-mp3/
2. Pure Instr input (using L5-CES)
https://www.tonstudio-forum.de/attachme … -320b-mp3/
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14