Keith Elliott, just designed an SD Card Holder that sits right on top of the PSIO SD Slot and adds room for 4 more SD cards.
Keith uploaded the design files on thingverse and made 2 versions available: one with an opening for the led indicator and one without it.
He’s also working on incorporating Firebrand X’s latest digital audio through Toslink into the whole shell.
Grab the files here if you’re interested: https://www.thingiverse.com/thing:3313614