Dave, with respect to the Horace Parlan "Us Three" MM 45 reissue, I had the same impression as you. The music is great, and the sound is dynamic/propulsive. However, the recording quality is mediocre in capturing the sound of the piano and inferior to the sound quality of some of the other Blue Note sessions.
I also have 33-1/3rpm LP versions of all these Blue Note Horace Parlan sessions (another Mosaic Records reissue box set). At some point, I intend to listen to some excerpts from both the Music Matters pressings and the Mosaic Records pressings to judge the comparative sound quality. I suspect that Music Matters is getting everything possible from the underlying master tapes but that there are some inherent problems with recording quality for some of these sessions.
I also have 33-1/3rpm LP versions of all these Blue Note Horace Parlan sessions (another Mosaic Records reissue box set). At some point, I intend to listen to some excerpts from both the Music Matters pressings and the Mosaic Records pressings to judge the comparative sound quality. I suspect that Music Matters is getting everything possible from the underlying master tapes but that there are some inherent problems with recording quality for some of these sessions.