Made the new setup today... Only the drums could be heard.
The good news: sounds like your guitarist can play at a reasonable volume.
Are you *all* hearing only drums, or does the drummer hear the instrument amps loud and clear—maybe too loud and clear? If you have the amps behind the drummer, as you propose in post #1, it's possible *he* hears too much of the amps and is bashing the drum kit to keep up.
OTOH, if nobody—including the drummer—can hear the amps (and vocals?) *and* the drummer is too loud in the room, then the drummer should be playing at a (lower) volume that supports the mix in your rehearsal room. If he's not yet good enough to play w/ feel at whatever volume is called for, then he either hasn't developed his touch yet, or he hasn't developed his ears so that he's listening and interacting with the other instruments. If so, that's your core problem—but maybe you can reduce the effects for now by arranging your rehearsal room differently.
In most genres, the audience judges how good your band is largely on the vocals, so make sure those are clearly audible in the rehearsal room. Unless you're using IEMs, the vocal mics will set the practical upper limit on volume—and in the typical small rehearsal space that feedback-imposed volume limit is pretty low. Even with perfect eq, there will be a maximum volume before the mics hit feedback. Any big peak in mid-range or treble response will make reach feedback earlier, so cheap mics through cheap monitors aren't your friend in the rehearsal room. But even a fairly flat-response monitor placed in the null point of a mic designed for high SPL before feedback will eventually start squealing, so use physics to fight physics.
1. Volume falls off with the square of distance. It's especially important the vocalist(s) can hear the vocals. If you just have one lead vocalist, move the vocalist away from the next loudest sound source in the room (which in your case seems to be the drums). If your room is longer than deep, put the drums by one short wall and the vocalist by the opposite wall. Get the vocalist's monitor in the null spot of the vocal mic, ideally lifted off the floor to be a little closer to the singer's head.
2. Treat the vocalist's mic position to minimize feedback. Even with the monitor wedge in the mic's null spot, the mic will still hear it some. Moreover, in a small rehearsal space, sound from the monitor wedge will bounce off nearby walls to cause feedback. The frequencies most affected will depend on the wedge/wall/mic distances, so you can fight this somewhat with a combination of placement, judicious parametric eq to notch problem peaks, more general eq to tame hyped monitors, and wall treatments to minimize reflections. If you're trying to squeeze every last drop of gain from mic-to-monitor, though, you'll have a very unstable relationship to feedback. Address any glaringly eq peakiness in the chain, and then dial back monitor volume a bit to give some headroom. If you're lucky, you'll have a fair bit of breathing room b/w reasonable rehearsal volume needs for you vocals and the feedback limits of your space.
3. With the rehearsal room's vocal volume dialed in, try vocals and drums together. Can both singer and drummer hear themselves now? If so, 4A. If not, 4B.
4A. *If* your drummer now can play underneath the vocals, set your instrument amps along the room's long wall. If drummer needs more than the singer, shift and/or angle your amps toward drummer's end of the room. If your amps are elevated, you'll be able to adjust the balance of what you hear by where you stand. If you mic/DI the instruments, you can feed a little into the singer's wedge to give your vocalist better instrument cues without boosting the volume level at the amps. (Remember, shorter distances are your friend. So a little bit more guitar for the singer happens most efficiently at the singer's wedge, rather than by boosting the guitar amp in the middle of the room.
Also, if you're using one of the digital boards (or otherwise have access to robust processing), use HPF and a little parametric scoop on the instrument voices in the singer's wedge. High-pass filters will keep the singer's corner of the room from turning into a bass swamp, and the parametrics can trim a little from the instruments' midrange to carve some extra space for the singer's voice.
4B. If the drummer in step 3 still *can't* play underneath the rehearsal room vocals, the standard TalkBass solution is to fire the drummer. Other possibilities include acoustically isolating the drummer (gobos, drum shield, or building a drum room in your rehearsal space), acoustically isolating the singer, moving the drummer to an electronic kit so s/he can happily bash away without destroying the band mix, putting the drummer in headphones fed w/ a loud drum mix (in hopes that drummie develops better touch control before going deaf), or giving vocalist (and other players) IEMs/headphones so they'll be isolated a bit from the drums while getting as much vocals and instruments as they need.
If going to headphones/IEMs, ideally get rid of as many through-the-air sound sources as possible w/o sacrificing tone. If you're chasing a flat studio tone on bass—or if you otherwise have gear that lets you get the tone you're after w/out a bass cabinet involved—consider going DI. Definitely get rid of the vocalist's wedge—and ideally lose all the monitor wedges to greatly reduce the chances of mic feedback.
Not all rehearsal session have the same goals, and if you're using different signal paths live, you'll want to use those amps etc. for some rehearsals just to practice listening to one another. But for bread-and-butter rehearsals that include some too-loud players, IEMS/headphones with mixes set for each player are the closest thing to a solution for the players in the band that want to hear a better mix without going deaf.
