another option is a cheap outboard mixer - I've used an old inexpensive yamaha MG10 for this for years - works great... no output module, the mixer handles modular levels well...
-- JimHowell1970
I've got a Yamaha MG8/2FX and I used to do the same, plenty of well-priced mixers on eBay too.
Enjoy your spare HP, don't rush to fill every last space, this is not like filling sticker books. Resist the urge to 'complete' your rack, its never complete so just relax.