Is this ok? Digital Out > Digital In?

I'm just asking the Apple group whether this is ok to do?

I want to record myself but digitally as its cleaner (with no artifacts!) from the SPDIF headphone digital OUT (synth program 1) back to the Mic Digital Headphone in (DAW program 2) on the same Macbook.

So in effect its just a looped digital cable going from the OUT > IN , hanging off the Mac.

I want to record myself seperately from one program to another "live" almost, and this above set up (although wierd!) actually works!!

I then output to my monitor speakers from my small seperate USB interface (which has 1/4" jacks for monitors) but it can't do the Digital record as above.

In my Audio MIDI Set up window, the Digital OUT and IN are both set to 32-bit float, but am assuming that this should record fine as its a digital signal with no degredation?

Is there any reason why I can't do this? It seems to work fine, but wanted other Mac users opinions?