"Years ago condenser mics varied in the amount of power needed. Each manufacturer set their own design requirements that varied between 9 volts to as high as 52 volts. Except for some specialty mics most modern condenser microphones operate in the 9 volt to 12 volt range. 48 volts is a standard not a requirement. The microphone will use only the amount of power it needs. The RMX 6 should perform fine in whatever application you need"
That's pretty much a lie. OK, I'll be nice and call it spin.
Condenser mics fall into two categories: externally biased condensers (sometimes called "true" condensers) and electret condensers. Electrets have permanently polarized backplates, so they are happy with just a few volts to run their internal electronics.
True condensers, on the other hand, need a high external voltage to bias their capsules. Most require +48V to do so. While it's true that a true condenser
could run off of +15V, it would require a DC converter in the mic, which increases costs significantly, and could increase noise without proper design. Since +48V is a standard met by nearly all professional gear, there is little incentive for a mic manufacturer to do that (unless their capsule needs more than +48V, in which case they would, but they might still expect +48V to step up to the higher voltage).
I'd understand if a portable bit of gear didn't do full +48V phantom, that costs a lot of current for a battery power supply. But if the thing plugs into the wall, c'mon, it ain't that hard.
Just for grins, ask the guy if all of the Nady SCM microphone series works on +15V phantom
What would I do? I'd sell the main board and save up for a used Mackie 1604 or something, those can be rackmounted. It takes a few more rack spaces, but you'll thank me later when you have a fully functional mixer.
Trust me, I went from running a Tascam Porta with
a Peavey RQ200 as a sub, to a 12 channel Peavey and finally a 16 channel A&H MixWiz. I mix with the Mackie at my church now, it can't touch the A&H (especially the EQ), but the used prices are pretty cheap. Eventually you realize it just isn't worth messing with a lot of toys cobbled together when you have a show to do.