Like you, in our band I'm not the bassist, but the bassist uses my DB and my DB's setup. From what I've seen with this situation, you set it up as nicely as you can, with as much flexibility as possible, and go from there. A person playing your DB has to either understand it's your DB and your setup, or have his or her own DB to play and make choices about. Our band's bassist is very talented and experienced, we feel lucky to have him, and I fully trust my DB in his hands, so I'm happy to have him using my DB. And he's expressed that he's very happy with it too.
Our band is primarily acoustic; while our instruments are bluegrass instruments we specialize in Gospel which can range in sound from bluegrass to classical, so our use of amplification for all our instruments and voices is in hopes to duplicate natural acoustic sound as much as possible. Not sure if that applies to your guitar trio...
With that in mind, on stage with an FOH my preference is to setup my DB using its mounted mic for a clear feed to the FOH. If necessary I'll also setup my small bass amp with my DB's piezo/pre-amp system to also use as a personal monitor, but usually it isn't needed.
If instead of an FOH we're working with my small sound system (which includes a small dedicated bass amp) or with my larger full PA, I'll try to use the mounted mic first because it duplicates acoustic tone the best. If the DB doesn't penetrate or if we need more sound separation, instead I'll use my DB's mounted piezo/pre-amp system, or I may also try to blend that with the mounted mic and put up with the added complication of wondering what the audience is hearing. When we use my larger PA system, I have a dedicated sound tech run it so we can concentrate on making music.
If I'm playing the dB myself with another combo, and if players in that combo are using amps, I'll use my DB's mounted piezo/pre-amp system. The point being, mics usually reproduce the best acoustic tone, but they are prone to picking up side noise and having feedback at higher volumes. Piezos are great for penetration and higher volume with less feedback and less side noise, but they usually contribute significant electronic tone. Usually if I'm playing with amp'ed musicians, my primary concern is penetration, not acoustic tone.
And lastly, I use wireless TX/RC units all the time on stage. I have two sets of them for if I need to run both the piezo/pre-amp and the clear mic feed at the same time. It is sooo nice not having to worry about cables with an instrument as large as a DB.
Good luck with your setup and gigs!
