With speakers, headphones or a digital receiver? If you clarify that I can advise on what you could use.
Assuming you mean the PC version of Bad Company 2, your Audigy 4 will work with surround sound speakers with an analogue connection.
If you want to use the Audigy 4 with a dolby digital receiver via a digital connection you will need the following software upgrade:
http://buy.soundblaster.com/_creati...ail&category=Software&pid=F2222SR6PAKH5DGY6SD plus any cables or connectors required for the connection.
You might need one of these to be able to plug in an optical or coaxial cable:
http://us.store.creative.com/Sound-Blaster-Digital-IO-Module/M/B002DS2IRA.htm but I don't know anywhere that still stocks them.