Some more thoughts on the setup (in addition to our DMs).
It sounds like you mostly have a problem with the number of sequencing devices you want to connect and the number of din ports on the mioXM.
I’m assuming you want the hapax, Atari, PC, Novation (and the TB-303?) all sending notes to your synth gear (and possibly some of these could receive notes as well).
Are you using splitters for the main output ports to the gear? That requires 2 din ports, then.
If you get two of these: mio — iConnectivity you get more din ports to work with for your routing. There are other options depending on how much you want to spend or your comfort with a soldering iron and arduino ide.
Okay, more din ports available.
Now you need to decide on how to route things, and this comes down to whether you want to use the hapax to route or not which also depends on how many midi senders you have.
If you have the hapax handle routing, you would plug all of your note senders into the hapax and for a given instrument, you would make a track that takes an input port and channel and sends it to the specific port and channel for the instrument.
So for the novation you could have one connection to the hapax and play up to 16 instruments across the two halves of your room.
The hapax has a din input, a trs input and a host connection. You could connect the novation through the host and have two more din ports for other sender devices.
One question here is if you need the mioXM for output at all. If you have midi splitters why not connect them to one of the 4 din outputs on the hapax?
This, of course, would require you to use the hapax for all of your routing.
If you want all of your midi senders to be independent of each other, go through the mioXM. This is also the only option if you want to send sysEx. Instead of getting more ports on the XM you could also use a less expensive merger in front of the XM, and again if you’re handy with a soldering iron, you could have lots of din ports pretty easily.