Ok Glyn - This is my situation.
My voice on Zoom is a bit boomy. In a windows pc there is no easy eq.
So to get round it I could use a mixer. Mic into mixer - mixer output into the PC line in. Apply eq to the mic channel - problem solved.
There is no reason why I could not plug up a BT input and my Guitar input to the mixer. There should be no delay between any of the individual inputs as they are combined in the mixer and put into the PC line it all together.
For the recipients they can listen and play along - but should turn off their zoom inputs.
I have not tried it yet but I think the recipients could record the zoom meeting but as their inputs are off it would not include the recipient.
With respect to bandwidth - slow internet etc. You could each turn off your camera - to release more bandwidth for the music.
Then again in the Zoom Settings you could set up stereo sound. It is there - I checked this out with BarryG. It worked ok. He is down south I am in Wales.
My setup has a Edirol 6 in 6 out. The main irritation is that without rewire software I can't get any of the outputs back as inputs.
So for my mic - I input through Edriol to my Daw and output from the Edirol is wired to the line in on my PC. So I apply eq to the mic. The Daw is running a project - initially with just one channel input and one output.
But of course I can import BT's into that project and they can be mixed and sent to the Edirol output and hence to the PC line in and so to the Zoom Input.
I tried rewire software - it all worked except with Zoom audio. I had clocking issues - realised I could sort is as above so gave up.
I hope this helps.