Efficient Connections

Looking for anyone with experience using the LR-16 with the Behringer Eurodesk SX2442FX. I have a 5 piece band and we are trying to determine how best to record our practice and live sets. We are using the following equipment; 4 vocal mics with XLR Connections. 2 electric guitars, with effects pedals. (T/S Instrument cables into “Line In” inputs). 1 Bass guitar, (D/I Box available). Keys with 2 channels required, (Preferably stereo, TRS Cables) and a DW 5 piece kit using an Audix mic kit, (5 Mics with 2 overhead condensers.) One of the channels on the board, (9) is not working, everything else is fine. What I need to figure out is how to get sound into the LR-16 from stereo channels beyond 16? My best guess is to send the keys, (Plugged into Channels 17 & 18) to a sub-mix (1 & 2) and then run the patch cables into Sub-Mix Out 1 & 2? I’d like to keep the drums in 7 channels so that we can process each input later in the DAW. (Logic Pro X on an iMac.) We recorded quite a few tracks today, but my hookups were a mess and unefficent. The sound was OK, but I’d like to improve upon that. We are using a 16 channel TRS to TRS snake into (and out of) the channel inserts, (I/O’s), with the exception of 15 and 16, which I’m hoping will work for the keys out of the sub-outs for sub-mix 1 & 2. What do you guys think?