What is the difference between the IC-25-6 vs. IC-25-2P cable?

The IC-25-6 is a 25 foot six pin male XLR to Female XLR 4 pair cable.  Meant for analog IFB control.  The cable comes in 25ft (7.6m), 50ft (15.2m) and 100ft (30.4m) versions.  Part #s IC-25-6, IC-50-6, IC-100-6, respectively.

When to use an IC-xx-6 cable?  If your design involves an IFB connection (MA-704 to PIC-4704).  All connections are wired – pin to pin on both ends.  This is a Mogami 2602 4 pair mic snake cable.
It is designed for use with the IFB system --- MA-704 to PIC-4704. It can also be used with the RS-602 and 622 6pin XLR belt packs.

When to use an IC-xx-2P cable?  If your design involves RS-602 RS-702, 622 (6-pin XLR belt packs).  The IC--xx-2P is a better choice at lower cost.  It is a 2-pair V flex with a clever “ cross-talk resistive” wiring arrangement.  IC-25-2P cable is VTG Audio 2 pair Ultra Flexible Professional Grade Multi Pair.

IC-xx-2P pinout.  This 2-pair cable comes wired as follows:

1 - Channel A & B grounds/shield 
2 - +30 VDC (for both Channel A & B)
3 - Channel B audio
4 - Channel A audio

Note: Pin 5 and 6 are not wired. There are no conductors in the cable to use.
Pin 5 and 6 are picked up at the pack using the parallel –daisy chain- connection with a dedicated 1 pair cable

IC-XX-25 pinout.  This 4-pair cable is wired as a straight 1-to-1 pin-to-pin cable.