I had it on good authority, before I bought my M6, from people who had owned/heard the Phoenix and at least one of the Master series amps that the bass is significantly better om the Master series amps.
A couple of Phoenix owners commented that the amp had to be warmed up for at least an hour before significant bass appears which is absolutely not the case with the master series.
Personally I feel the bass on the M6 is superb with plenty of tight controlled punch if it's on the recording.
Hopefully, possible, as i like the bass on ref. 7.1 a lot.