I have a RME _PCIe_ Raydat card that is supported by Linux. It has 4+4 ADAT ports, meaning 32in+32out channels. You can connect basically every interface that has ADAT to it. I've connected two Ferrofish Pulse8 AE, a Focusrite Scarlett and a Motu Traveler. :-) If your UA Apollo has ADAT, you still can use it this way! Of course it hasn't to be a RME Raydat, any other Linux supported interface with ADAT does it too, f.ex. a Scarlett. You could get a cheap Scarlett and connect your Apollo to it. Hahaha. Seriously, this would work.