Having the file is the first step in removing the DRM - you can set DeDRM up as a plugin in Calibre to strip DRM automatically when you add the AWZ3/KFX file to your library.

I find stereo mixes are better for more smooth audio levels - if you get a surround mix (assuming you don’t have a surround sound system), then the centre channel is too quiet in the downmix. You might be able to boost the centre volume, which depends on your setup.

I mostly use private trackers, and normally the only stereo is in multi-track releases so you will waste a bit of storage there (plus they tend to be larger, high quality files).