yeah - not a bad go - not a fan of xpan or rosie - do you really need crossfading? I'd go happy nerding panmixjr/stereo mixer instead and a 2hp headphone module

which would save 4hp with the 3hp you already have free - that gives 7 which is a pain - something 4hp and something from the erica pico series - or maybe 2 2hp modules - maybe they do a crossfader if you need it

you might want to update your maths to a more modern version - the one with white knobs is the latest!
-- JimHowell1970

Thanks for your reply !
I hadn't checked the math version.
The Rosie got me with the send in/out but the matrix mixer could do it too. I'll dig the output modules.