1). If you feel the need to stay together as a unit, you have to find a way to rehearse together on a consistant basis, or he'll ALWAYS be behind and never get tight with the two of you when you play together.
2). Does he take lessons? He needs to hook up with a really good SET drummer and learn time-keeping techniques and also learn the importance of dynamics. That will especially include playing quiet. The quieter you start out, the more you can make the dynamics you use in the song stand out.
3). You all have to treat this as a "business". If you want to play music gigs, there has to be a business aspect and attitude to the performers. This also means that you all promise to make your best effort to play your best and always get better. If that isn't happening, then any, and
all three of you are each expendable, and need to all realize that for the good of the band, any of you could be let go for a better player if conditions aren't met by all. (Maybe that will get his attention...)
I assume that you're a younger group and you have plenty of time to get your "groove". It won't happen, though, unless you all three can rehearse together. Once that happens, then there will be things, (like tempo, volume, etc.), that will become apparent and you will have the opportunity to address those issues in a rehearsal.
Remember; presentation is everything! If you want to bring it up, try something like; "hey! I noticed that I'm having a hard time hearing the vocals, (or whatever), during this song. Let's try everyone backing off of the volume this time and see how it sounds."
Then there's no finger pointing at anyone, and if it works, then you can suggest that you continue the volume reduction for a while and maybe he'll get the feel for it.
That's about all I can think of for now. Good luck!
