Yeah, you can use em. I don't know which speakers you are considering. Their bookshelf speakers would generally be the better choice as their floorstanding speakers are about the most inaccurate speakers I can think of. The bass is unbelievably hyped and any "mix" you might capture off of these would not translate very well, if at all, to other systems.
Ive gone down this path as well and, many many years ago, when I transitioned from my pair of Sony bookshelf speakers to a set of decent monitors (EV MS802), it was literally night and day. While I could get decent mixes off of the Sony's, the EV's made it so much easier and faster that I kicked my self for not trying monitors earlier. My mixes were of a much higher quality because, well,
you can't mix what you can't hear. The detail that was missing from my earlier mixes (nuances such as string/fret noise, key clicks on horns, even the breathiness of a vocal) was suddenly revealed with monitors.
We can mix, theoretically, on almost anything as long as we know how those mixes translate and how to compensate for the speaker systems shortcomings/inaccuracies. But, that doesn't mean it's an easy or worthwhile process when, even a inexpensive set of monitors, can make the mixing process much more efficient and effective.
As for cables, I'm assuming you've got 1/4" outs on the interface and the stereo amp has RCA inputs. If so, the just get a pair of 1/4" to RCA adapter jacks.
http://www.audiogear.com/cgi-bin/shopper.cgi?key=Adpt-QMFRCM&preadd=action
Run your 1/4" cables out of the interface and plug the adapter into the amplifier.
Good luck on your monitor search...let us know what you find.
