Why do you want to put the splitter by the sound person (FOH)? You will STILL need to have jumpers going from 1 side of the splitter to the FOH, as well as the snake going to the CR. Maybe 3 feet long, but still...
Generally speaking, you want the mics cables to terminate at the splitter box as soon as possible. Usually this is 25-50 feet onstage. Then you use the splitter to "drive" the signal to the FOH and the CR. The longer the mic cables to the splitter, the more likely you are to have a signal loss issue and the potential to pick up stray RFI. That said, 100 feet should be fine.
Actually the bigger question is: what type of splitter are you using?
There are 3 basic types:
1) The DIY (do it yourself) approach, championed by many local sound companies, is to take a couple of "splitting resistors" to make each mic split work. No transformers or fancy IC's for these guys! Cheap'n'dirty, they are notorious for noise and signal loss problems. 50 feet if you're lucky!
2) The "active" type. This does use a small opamp type of circuit to balance the signal. Various versions, some quite good, others not...
3) The "passive" type. This uses a real audio transformer to do the job. Various forms of this, too. But this will usually yield the lowest RFI issues, and be the most reliable. These can drive up to 600 feet without worry.
From what you are describing, though, you still don't have more than 100 feet on any leg of the splitter at one time, do you?

ringo, you really don't have to worry about the loss in the cable. Even at 175 feet, it's not a factor with low impedance microphones and keyboard feeds, etc..

My audio regularly goes up 250 feet to 500 feet on average without problems. At that length, my loss might be 1 DB at 15kHz? Like I said, not a factor. What does become a problem at those distances is the phantom power supply. Phantom power is DC and DC does not travel as robustly as AC, like the microphone signal. What I really wanted to construct was a master input box/splitter/phantom power supply. That is to say, I would like the phantom supply to be as close to my microphones as possible to supply maximum voltage and current, for the 2 or 3 condenser microphones I use. Thus far, I haven't bothered to build it, since front of house is closer up the snake and so provides good phantom for those few microphones on stage that require it. For those other occasions where I am 250 feet away from the microphones, my Phantom has worked just fine.

Preventing ground loops. That's a factor!

Coordinating with the FOH guys who is going to supply phantom power. That's a factor.

Generally, I'll let the FOH provide phantom. That way I can turn mine off. You can have problems if you continue to supply phantom, while they are also trying to.

Good microphone preamps make the biggest difference, not the cable.

Pretty in long snakes
Ms. Remy Ann David

splitter type

mb - though we have plenty of room, I was mainly interested in getting the stuff off the stage - not necessarily to put it by the house mix. Thanks for your help - you too RemyRAD- glad that I found the forum!