I should have been more clear.
The M4A files I am sending are entire mixes where I have removed the original bass guitar from the song (via stem separation) and replaced it with my bass recording.
I'm not passing (sending) a bass track but rather an entire mix made up of guitar, keys, sax, vocals, etc., and my bass recording.
This is what I mean by "bass overlay recordings".

Here is an example (not me).
Bass Overlay


https://soundcloud.com/user-646279677
BiaB 2025 Windows
For me there’s no better place in the band than to have one leg in the harmony world and the other in the percussive. Thank you Paul Tutmarc and Leo Fender.