I'm currently using sonar pro and a presonus ione interface. Is it possible to record and monitor through the interface but still have all sound playing back through my computer? I only have headphones to use with the interface and it seems to be causing panning issues; when I pan either left or right, instead of actually doing any panning it just increases the volume of the track, which is not an issue when playing back through my computer speakers

Not if you are using ASIO. That allows only one active interface at the same time. You could use another method (I'm not sure what it is called as I'm not at my DAW) that does allow it to do this.
 
However, usually when you just increase volume when panning, it means your headphone connection is either receiving a mono signal (which then just increases or decreases the total volume as it adds both channels), or the cable for your headphones isn't plugged in fully, which basically also results in a mono signal (as it touches both 'pins' in the connection at the same time).
 
I would check if your interface indeed has a stereo headphone output (which I would think it has, but it doesn't hurt to check) and if it does, maybe a setting in your audio interfaces control settings is not set correctly. And lastly, if you are using a bus to send your mix through to the headphone output (if possible) check that it isn't a mono signal.

For playback through the computer, there's a little plugin I posted here:
http://forum.cakewalk.com/Tip-when-travelling-with-no-monitors-m3395736.aspx
Just put it in your master bus....

a couple adapters and you could hook them up through the "Main outs" on the back of your IONE.
(A 2 prong stereo Male 1/4 apt to an 1/8 female)
 or run a stereo 1/4 male from your headphone jack to a 1/8 female for your PC Speakers.

Nice one man, turns out the 3.5mm to Jack adapter I was using for my headphones was faulty. Luckily I had another lying around and it works perfectly now, no need to play through my computer speakers. Thanks again!

But as Chuck said easy enough to unplug your headphones and plug the computer speakers instead. Unless the connection is hard to get at all the time. In that case a little extension cable running the back of your CPU.