I apologize for the general nature of this post, but I just built my first computer and have researched a TON and want to make sure I haven't overlooked something. 

-I am centering my system around two sets of Alesis HD24 ADATs (48 channel adat i/o total, 48kHz 24 bit) and an RME Raydat PCIe card with the typical expansion daughtercard. 
-I have a moderate amount of analog gear (nice preamps, useful compressors, great river EQ, lexicon reverbs, etc.) running through some Allen and Heath ZED boards, fully analog with TRS direct outs.
-I just built (first time builder! haha) a Windows 7 Pro computer running:
    -Intel i7 3930K 3.2GHz Processor
    -48GB Ram
    -Two 128GB Crucial m4 SSD's
    -ASUS P9X79 Motherboard ... onboard Realtek audio card with optical S/PDIF out

I guess my main question has to do with the use of the onboard audio card of my motherboard.  Is there basically no use for this when I have my Raydat?  I use Reaper DAW and when I set up my audio devices, I choose ASIO which gives me no option to use anything but the Raydat.  I've heard mention of ASIO4ALL but I honestly have no understanding of it yet or what it does.

Basically, am I forced to use let's say CH's 1-3 of the Raydat for tracking INPUT and use CH 4 for OUTPUT back to my analog gear/headphone amp?  And then when I want to use my analog gear for analog summing before mastering, I would switch things and use CH's1-3 for OUTPUT to the analog mixer and INPUT the signal back to Reaper with CH4 of the raydat?

I'm ok with this, I just wanna make sure there's no way to get the extra I/O from the onboard audio in the PC.

Thanks!