This is probably probably opening a can of worms, but in terms of
sound quality and flexibility, I've found using plugins in a DAW for
mastering works better (I actually use LinuxDSP LV2 plugins and
MixBus).

I 2nd everything stated above. I used Jamin with A2 for a long time for mastering, and it worked really well. I then went to mixbus and found the LinuxDSP suite of LV2 plugins to be exceptional (para-EQ with mult-band compressor). Works like a charm.

--Jason