ProCo MS-42 4-channel microphone splitter, circa 2004

These currently sell for around $450 ea new on B&H here:

Manufacturer info:

The MS-42A from Pro-Co is a rack-mountable four-channel microphone splitter that splits four low-impedance microphone signals into two outputs, allowing two mic preamps to be fed from one source. The MS-42A is ideal for use in stage monitor systems where an on-stage mixer is used or in recording applications where PA system microphones must also go to a recording mixer. MBT-1 transformers in the MS-42A provide protection against interference and offer low-impedance outputs with a wide frequency response and low distortion. Ground-lift switches combined with these transformers provide buzz-free operation in practically every environment.

The MS-42A uses standard 3-pin XLR connectors for quick and easy hookup with your system. A rugged steel and aluminum Uni-box(TM) construction provides long-lasting durability. For quality audio and construction in a rack-mountable design, the MS-42A is a great choice.

Splits four low-impedance mic signals into two outputsIdeal for on-stage monitoring and remote recordingConnects with standard XLR cablesFront-panel connectors for easy accessHigh-quality transformer-isolated outputsRugged Uni-box(TM) construction for strength and durabilitySingle rack space unit

Note:

I have two of these units available. Please contact me if you're interested in buying both for a discount.