Whoa there, Ladybear!
For your first composition, this was very nice. You've displayed a great feel for layered melodies and instrumentation. The marimba (or, I believe that was a marimba) was fantastic, and really kept me listening. It was just... Calming. Yet somewhat driving, and uplifting. Eliciting that sort of emotion in a piece can be difficult, but you did very well.
That said, there are definitely many areas you can improve.
1. Mastering Mastering Mastering!
Though Edirol may not have the highest quality samples, you can still touch things up a lot with proper mastering. Adding reverb is one great start. With the music being as damp and breathless as this, it can actually make my eyes water when wearing headphones - and that's not pleasant.
Experiment a bit with the Mixer, using things like equalizers and reverb and all that other fun stuff. It'll add a huge dynamic to your music, making even lower quality samples sound professional.
Another huge problem here is too make sure you don't turn Edirol up too high. I'm not even sure if this was the problem, but the buzz that started coming in around 2:10 was awful. I've never had the issue, but I'm assuming it has to do with the settings on Edirol. It's better to turn everything down and just raise the Master Volume when you export than to try to turn certain instruments up too high.
2. Melody.
You did have great melodies here, I won't deny that. However, they either vary too much or too little for them to be memorable. The marimba was fantastic, but the way it switched up made it more difficult to follow and much harder to remember later on. I've listened to this song about 4 times now, and a couple of hours later I can't remember much about it. Heck, I'm still trying to remember a lot of it. :L
The best route to take there is to either capitalize on one particular melody and make it simple, even repetitive; or to pick an instrument to really bring out, and move it along through several captivating melodies. You did a decent job of both to some degree, and I'll admit it's a lot easier to correct this stuff in hindsight, but I really feel like you could improve that aspect a ton.
3. Limit your instrumentation a bit.
This kind of goes with the melody. You had the strings trying to take melody along with the mallets, and it honestly took away from it. If your melody is primarily mallets, try to keep the strings simple - moving along as a chord progression more than as a melody of its own.
I'm sorry for the lengthy review, and I'm especially sorry if I sound harsh. This was actually VERY good for your first (I presume) piece, and I really look forward to hearing more from you. :]
PM me if you have any questions!