Available as an assembled Module and as a DIY project.
This Module is currently available.
6-way passive multiple
It doesn't really get much simpler than this - a 6-channel passive multiple to fill that awkward little gap in your case.
Supplied with a laser-engraved panel fabricated from 1.6mm FR4 (PCB material), mounting hardware is also supplied in the form of M3x6 machine screws.
https://www.yorkmodular.co.uk/products/pmult-6-way-passive-multiple-2hp
