@gwpt welcome to the forums and thanks for your interest in the MatriX!
Yes, the MatriX can connect to both a SEQ v4+ and a LoopA at once - it has two BLM-Ports for that purpose.
There is an A/B button on the frontpanel that allows you to very quickly switch between both connected sequencers - in this quick demo video you see it as the green illuminated switch below the joystick:
The color indication of that button (green/red) indicates which sequencer is currently active.
We’re yet working on the software for the MatriX <-> LoopA connectivity and on the MatriX manual, more infos will be available when that is done 🙂.
Best regards and have a good upcoming weekend!