You can get a digital EQ like the Behringer DEQ2496. Go optical from your Apple TV to the EQ. And then go optical from the EQ to your Peachtree.
I'm not sure that will fix your problem, though. If you tried the EQ in itunes and it didn't give you the bass you need, I don't think an EQ will fix your problem. I know the resolution is less with itunes, but for bass, it should have worked. Looking at your system, I think you are under powered. Your amp is probably having a difficult time driving the low frequencies. One thing you can try, if you have the room, is to move your speakers closer to the back wall. If you need just a little more bass, there's a good chance moving your speakers will work.
I'm not sure that will fix your problem, though. If you tried the EQ in itunes and it didn't give you the bass you need, I don't think an EQ will fix your problem. I know the resolution is less with itunes, but for bass, it should have worked. Looking at your system, I think you are under powered. Your amp is probably having a difficult time driving the low frequencies. One thing you can try, if you have the room, is to move your speakers closer to the back wall. If you need just a little more bass, there's a good chance moving your speakers will work.