Apogee audio interface better than a DAC?

I recently installed an Apogee One on my iMac so I could record guitar in Garage Band. Which it works well for. What I was surprised to find, however, is that now my studio monitors sound much better. (They were previously just plugged into the computer's stereo output jack.) In fact, out of curiosity I added Decibel to replace iTunes and man! I'm not certain, but the iMac/Apogee/Jamo system in some respects is superior to my Audio Research / NAD / Green Mountain Audio main system.
The computer system is very clear and revealing, which I guess a monitoring system is supposed to be. But it isn't off-putting or headache-inducing like I would expect. (Although I haven't sat there and listened for even a full hour, so maybe that's to come.)
Has anyone else noticed their relatively inexpensive home recording studio is a top-flight hi fi? I'm wondering how to use the Apogee in my stereo, but I don't think it's possible.
I use an apogee USB duet two for recording and playback and my system sounds great. I record vinyl to my computer. Can record and playback up to 24/192. Works well with pure music.
How are you sending the digital information to the Audio Research? Through the mac's optical digital out? If so are you using a old/cheap/too_long digital optical cable? Those can introduce quite a bit of jitter into a signal.

I've got the original firewire Duet that I use for a guitar interface and desktop/onthego listening. Awesome piece. I love it for the big circular volume control alone!

I'm not sending anything from the Mac to the Audio Research. They're two separate systems. I was trying to point out that the computer system was surprisingly good compared to the hi fi rig.
The Duet has two inputs. Alas, the One has, unsurprisingly, one. So I can't use it to record anything in stereo. However, it does output in stereo, so I could conceivably use it like a DAC, so long as the stream that feeds it is USB. Another mystery to unravel. I might be able to plug my iPod into the One's USB inputs and see if it will send a stereo output to the Audio Research amp. I'll have to try this sometime.
I'm glad you guys like your Duets. I'm pleased as punch with the One.