No Problem! 🙂
I'm running 4 tracks of audio from Stage Traxx (ST) on an iPad - stereo backing track, drum click, cues.
My band has a Behringer X32 rack mixer that we use for our IEM system. I have the iPad connected via USB cable to the USB in on the X32 which exposes digital inputs in the X32. From there, I route the backing track channels to Front of House (FoH) sends and into our IEMs. The drum click only goes to our drummer's IEM bus. The Cues only goes to the band's IEM buses.
The Roland SPD is connecting to ST on the iPad via MIDI.
We do also still run some live drum samples from the SPD and so the SPD does have audio outputs running into our X32 mixer to be fed to IEMs and FoH.
I'm using CME wireless MIDI gear, but can fall back to physical MIDI cables if I need.
Simply, MIDI out from the SPD (i.e. your Alesis) going to the MIDI In of a MIDI interface that connects to the iPad running ST via USB (this is the specific MIDI interface I'm using - https://www.cme-pro.com/h4midi-wc-usb-host-midi-interface/)
Once the MIDI connections were setup, I just had the drummer setup the pads on the SPD to send a MIDI Note On when triggered. Then go into ST Settings -> Assign Action (ST doc link - https://stagetraxx.com/user-guide/remote/#midi) and press the specific action I want to 'link' to the specific drum pad. Once it is waiting in learning mode, hit the specific drum pad you want to link to that action, and if you've got everything connected and configured correctly, ST should receive the MIDI Note On command from your Alesis. Repeat the process for any other commands/pads combination you want to setup.
One 'challenge' we found that we had to consider with the Roland SPD (might be different on the Alesis) was that the MIDI send configuration for eaach Pad had a global setting, and a Drum Kit (i.e. a patch) specific setting. The global setting always 'overrules' the pad specific setting. So that was great for common triggers we wanted to use such as Start/Stop Plaback which we always wanted to be on the top left pad irrespective of which Kit the drummer had selected (because he still uses different kits to trigger different drum samples live from his SPD). But we have 1 song where we want to use the 'Initiate Crossfade' trigger. Now that is something that could be dangerous on other songs if it was accidently hit, so we wanted to be very careful and delierate about which pad we used, and we didn't want it to be a global setting available on every Kit (i.e. song). So for that song, we made a specific kit, configured a specific pad for 'Initiate Crossfade', and had to make sure it was a pad that doesn't have a global MIDI setting.
I think that's pretty much it, but if you have any other questions, fire away.