The 25 pin D-Sub connector fits on the back of the IF-AN 24, sending out 8 channels to or from your patch bay / mixer, either balanced jacks or XLR female or / male.
3 x 25 pin D-Sub to 8 channels inputs & outputs so 6 multicore looms in total. You probably only need one 25 pin D-Sub 8 way multicore loom for the recording inputs if you are recording 8 channels or less at one time, as you can actually assign the inputs to record on any channel.
The Tascam MX2424 does indeed use the "Tascam" pinout for both Analog & AES. Be aware that the AES & Analog pinouts are very different because AES send 2 signals down one pair. Therefore you get 8 ins & 8 outs on one Dsub25 However there are others, which fortunately are not so common now. Harrison has a pinout that is GHC in triangles from pin 1. i.e starting at the other end of the connector to Tascam. Yamaha has a completely random pinout for one of their boxes. Dolby has a weird pin out on some of their bixes, Euphonix used a different AES pinout to the Tascam one (guess how I found that out).
It pays to read the manual for anything you are connecting or face the possibility of having to do things twice
The Tascam AES 8 way 25 pin D-Sub wiring are the same as Digidesign / Avid Pro Tools. I've got the Digi branded AES cable loom going to the Tascam IFAE24 AES interface on mine.
An AES standard which defines the use and pin-outs of 25-pin D-sub connectors for eight-channel balanced analogue audio travelling in a single direction in or out of a device, and an alternative bi-directional eight-channel digital interfacing (four AES3 threes in each direction). It conforms...