The rampage has a pretty good sound card built in. Asus calls it X-Fi which indicates it is some sort of creative product. Probably the cheapest sound card better than that is an X-Fi titanium which runs about $80.
I'd say stick with your onboard. Also with a mini motherboard like the Gene you might want to make sure the card will fit. If you're using a dual slot card in the first slot it looks like the pci-express x4 slot would be covered
It is actually a stupid special Realtek sound chip with special X-fi software and such made just for the chip. The software is not true X-fi and after testing the sound quality, sucks compared to my Audigy zs 2. I just can't get the mic to work on the sound card with win 7. That is the problem