You can probably find plenty of converters. Google is your friend. The most usefull, in my opinion, is the RF to IR converters though. Then you can have a RF remote to be used anywhere. In other rooms, from your garden etc. You would need to place the converter(s) in a positions so the IR beam hits all your equipement though.
There's alot of possibilities when it comes to remote controls. You want LCD screen or not, a all directional mouse control or only up/down and left/right control. It is also nice with 2 way signaling so you can get coverart and playing now info etc. But that means getting a WiFi remote or possibly a bluetooth. With the WiFi they tend to be expensive.
If I were you, I'd go to
remotecentral.com and look and ask around. They would know more than me.
The last time I bought a remote was a Philips TSU 7000. An expensive but really nice remote. I got ripped off though
After that I have not been thinking much more of remotes, untill I saw this baby:
http://www.gyration.com/en-US/OEMProduct.html. I'll test out the Gyration around this summer. Looking forvard to test the mouse control. It's not very expensive either, and got RF signaling.
As far as the Audigy2 remote, I have no ide. Never tried it.
What sound card you use is up to you. I'll go for a Creative SB X-Fi my self. After the drivers have gotten better that is.
I would think that most soundcards beat the onboard versions, even if you have a older reciever. But it's up to you where you want the good sound. You'll probably not notice much difference anyway.