When input capacity of Instrument inputs is too low, then the sound can become muddy, less of treble.
Therefore the input capacity should be over 450 kOhm.
A good value which you find nowadays in more modern interfaces is 1 MOhm and this should fit for most if not all pickup types. I personally do not see a benefit in having a poti to change the input impedance of this instr input.
A good fix value should be enough.
Another thing .. there are so much more important aspects for a recording interface ... driver quality and long term support, low latency, no 3rd party communication chips whrere bugs can't be fixed (RME's FPGA based design), ...
Also from operational perspective TM FX is much advanced compared to what the competition sells. See Antelope reviews, even companies like them selling expensive gear are regarded to have bad software and support.
TotalMix FX is there .. ONE version for ALL RME recording interfaces ... in around 20y it reached a big MATURITY that other devices from competition are simply missing (because often there is a dedicated software bing developed only for the (short) lifecycle of such a device). I often read about laggy operation software and stuff like that. This does not happen with RME ...
So .. to make a long story short ... for me this AXE I/O is nothing that can compete with RME in any way. But this is simply an assumption based on experience and gut feeling and putting some facts together ....
As I said .. run it side by side and then compare.
BTW .. I wrote a blog article which addresses many of these points: https://www.tonstudio-forum.de/blog/ind … B-MADIfac/
Could be of interest for you to get a good overview.
BTW2, another blog article could also be interesting to you .. I also play guitar and I am very successfully using the instrument input of my UFX+ for different use cases which I described here and with sound samples: https://www.tonstudio-forum.de/blog/ind … -DURec-DE/
No issues with any guitar that I own: be it jazz guitar, Les Paul or Tele (Single Coil).
BBF Pro and BBF Pro FS also have 1 MOhm Instrument inputs (same as UFX+).
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14