Here are the pin outs of the MUX-25 radio ports and repeater/controller connector.

DB25 Female (repeater/controller) connector:
7 = Ground
8 = TX Audio Digital (to digital modulator)
9 = TX Audio Analog (Allstar analog audio to voice modulator)
10 = RX Discriminator / Detector Audio
12 = RX Audio Ground
16 = PTT (Active Low)
19 = TX Audio Ground
25 = RX COS (Active Low)

Digital DB9 Female:
2 = TX Audio from Digital Radio Adapter
3 = COS to Digital Radio Adapter
5 = PTT from Digital Radio Adapter
6 = RX Audio to Digital Radio Adapter
8 = Ground for audio and logic signals
(The digital radio adapter referenced is the outdated Satoshi AMBE DV - something else should be considered)

Analog DB9 Female:
1 = TX CTCSS from Asterisk Radio Adapter
2 = TX Audio from Asterisk Radio Adapter
3 = COS to Asterisk Radio Adapter
5 = PTT from Asterisk Radio Adapter
6 = RX Audio to Asterisk Radio Adapter 
8 = Ground for audio and logic signals
9 = +12 Volts for powering the audio amplifiers of the RA-35/40/42
(This pin arrangement matches the Masters Communications RA / RL pinout)

J4 = Power (12 Volts DC) as per the silkscreen.  Pin nearest J2 is Positive (+).

Refer to sheet two for jumper settings and additional notes on using transmitters with one modulator audio input.  
This board was intended to be used (primarily) with the Kenwood TKR-750/850 series repeater, but will work with 
other radios or repeaters if configured correctly as per sheet 2.