You said that you're already getting her speakers, right? Don't go for speakers and an ipod. Speakers are cool as a side gift because thats like a practical gift.
Gifts to girlfriends are differnet that gifts that we as men like to get. We want sh!t to play with. Gifts to a girlfriend should have meaning in some way. Or you must put meaning into the gift. Speakers do show that you know she likes music (which I'm assuming because of the joint speakers/ipod thinking). If she doesn't like music, then you're way off base!
The only way an Ipod would go well with the speakers is if you were to preload it with a bunch of songs and custom playlists that have signifigance. For instance, some would be music that you know she likes, but you can't stand (and she knows that too). That's one playlist. Then there's the 'you guys' music that has special meaning to the two of you. And the third could just be other crap. Maybe she likes excerise music or party music or maybe its just stuff you think she should listen to. Whatever, thats not the point. The point is is that if you get something like an Ipod, you have to make it mean more than just a portable music player.
Thats a lot of work, tho. Jewlery (not necessarily rings, bro) innatly have meaning to women, when recieved as gifts from the boyfriends. Find something that you think she would wear, but something different than what she normally wears. Tell her you thought she'd look great in it and that you knew she had nothing like it.
Thats how you work the gift angle to girlfriends. (The delievery of the gift is a whole other area that you must work out-but is equally as important, if you are trying to make an impression). (actually, that is an important part. All of this post is assuming that you really want to do something cool. that you're not just looking for an easy out, cuz if thats the case then just get the most expensive thing you can afford at tiffanys and be done with it).