I'm using a matchless too with RME and Logic. Bought it also 10 months ago and only now I'm starting to use it.
First of all you have to figure out what you want to do. If you want to record and mix 24 channels analog, you can do that. If you're only recording 4 mics than it's easy. If you want to use as much as you can, it's a little more complicated.
A little piece of advise: read the manual of the matchless and learn how to use Logic. Especially the way the routing systems work, both on the console and your DAW. On the matchless you use the routing buttons on the top of the channelstrip. We call these routes busses. You can send to a certain buss and receive it somewhere else. On the console that's 1-24 and ST. Whatever button you push, its sending the signal there. So 1-24 is sending to the direct outs on the back of channels 1-24. For example you can use channel 12 and route the signal to the direct out of channel 1. The red colored button is for the channel's own direct out. ST is for the master. So you don't have to send to the master if you don't want to. Now, a thing you have to know: when you use routing buttons 1-8, the signal is also going to subgroup 1-8. These subgroups are used for grouping i.e. drums, guitars, vocals. So you can mix them together and give them some overall compression, fx, whatever.
In Logic you can do the exact same things. There you use the output routing near the fader in the mixer window.
Now, how to connect. If you want to mix on the console, at the end you have to record the master outputs. That's your final mixdown. Some people do that on a dedicated machine, like a separate recorder. Myself (and many others), I do it just by recording back again on the inputs of the RME. So then you play your DAW, send it to the line ins on the TAC, there you can mix it and do whatever you want; use fx and compression or tweak the eq. Finally, the mixdown comes out of the back of the master channel. These outputs are going back to 2 inputs on the RME (just to converter channels, no use of rme preamps again!).
So if you have these RME inputs already connected to the direct outs of the Matchless, you have to get them out of the console's direct outs an use the master instead. That's a xlr cable by the way.
Almost every studio recording and mixing analog uses a Patchbay or Jackfield to connect all the gear. It allows you to route the signals in many different ways and most important: use compression, gates, fx any way you want. But that's a different story. First let me know how far you can come with the story so far.
You say you have the original manual? Can you maybe look something up for me if you have the time? I'm missing a few pages!
Good luck and have fun!