DDJ-1000, Rekordbox Laptop, Streaming Laptop and Sequencer / Drum Machine

I'm currently using the setup described here to (successfully :) stream: https://forums.pioneerdj.com/hc/en-us/community/posts/360061750192-DDJ-1000-WITH-2-LAPTOPS-AND-OBS

That is, I have:

*  A performing (Mac) laptop connected to USB-A on the DDJ running Rekordbox

*  A streaming (Windows) laptop connected to USB-B on the DDJ running OBS + Aiso4all and some Aiso-specific OBS plugin

I'd like to add a sequencer / drum machine for some layering / live improvisation and be able to EQ mix it in via one of the channel inputs on the DDJ.

Sometimes I will want or need sync (i.e. using midi clock to sync drum machine's tempo with tracks playing in rekordbox) though and I'm trying to understand if it's possible to use Ableton link to achieve this while keeping my current setup (which occupies both USB ports on the DDJ, currently).

Assume I have a sequencer (part of this is figuring out which one I want / need - so no brand or model yet) with both USB connectivity and a master phono output.

Can I hook the sequencer up to the performance laptop (via USB) running Rekordbox and Ableton and have it sync that way, connecting the phono output of the Sequencer to one of the phono (channel) inputs on the DDJ?

Or, would I need to unplug the streaming laptop from USB-B on the DDJ and connect the USB of the sequencer to USB-B on the DDJ, and then set one of the channels to USB-B input?

In that case, I guess my only options would be:

1) run XLR out of the DDJ and buy an audio interface for the streaming laptop that will take XLR inputs

2) Do some audio-interface-fu on my mac using Soundflower + some kind of hardware that exposes audio output that the streaming laptop can consume via a USB connection?

Or something else someone can suggest?

Thanks!