There are no problems at all with using the MC100 with the 244. Use the ¼” output with a standard ¼” plug. The cable should be ¼” on one end and RCA on the other, which I’ll explain in a moment. The output of the MC100 is balanced TRS, but using a cable with a standard ¼” plug will bridge the ring and sleeve as it should to make it suitable for the unbalanced input of the 244.
You also want to bypass the pres on the 244, so remove the jumper for the Access Send/Receive on the back of the 244 for the channel you want to use. Plug the RCA side of the cable into the RCV (Receive) RCA jack. You’ll be bypassing the first stage preamp and trim control on the 244. Otherwise you’d be using the external pres on top of the 244’s mic pre, which defeats the purpose of using an external pre. You can plug it into the regular ¼” input on the 244 and just back off the trim control, but you won’t be getting the straight sound of the external pre without the coloring of the 244 pre.
The signal also bypasses the channel overload LED on the 244 so adjust your levels with reference to what the MC100 is telling you as well as the VU on the 244. The signal will come in right before the EQ section on that channel of the 244.
Set the channel input slider on the 244 to nominal level between 7 & 8. Start with the output control on the MC100 set to minimum and then bring it up until it’s where you want it on the VU meter for that channel on the 244. The output control of the MC100 will now be you trim control for that channel of the 244.
I once owned the 244 for a while, but soon upgraded to the 246, which I still have and have owned since new. It’s a bit easier on the 246 because it has a couple line inputs that bypass the first stage and the trim control.
That Behringer MC100 is not a bad little unit… to my surprise, and for the price, you can hardly pass it up. Do yourself a favor though and replace the stock 12AX7 tube with a JJ Tesla ECC83S.
Bottom line is you have an output control on the MC100 that you can turn to zero, so you can't damage anything on the 244 as long as you don't crank everything to max. And even then the most you'll probably get is sucky sound until you back the levels down to a reasonable signal.
Best of luck