Well, 43 C isn't that hot. You said it spikes when you play mp3's, so does it get hotter than that and by how much? You should definitely use the thermal grease. I know it seems like a pain but i'm told it really helps, although I don't know that it's true. Make sure you don't get too much on though as it will only make things worse since it can tend to form a heat shield. You only need enough to fill the microscopic cracks between the processor and heatsink.
As for the fan setup. Sometimes you can have a setup that doesn't get much air flow around the processor itself. Although it seems that it works, sometimes you will have one intake fan blowing directly to an outtake and the air doesn't actually circulate that much. Also, watch out for ribbon cables obstructing the flow of air. Unless you have seen that type of fan setup recommended somewhere you could try switching some things around. Maybe get your aeronautical engineering degree first, that way you can be sure it will flow correctly.
Anyway, put the thermal grease on, and try it, if it's still too hot for your tastes, try a different fan configuration. For reference, I have an Athlon 800 with one heatsink fan, the PS fan, and another exhaust fan out the back directly across from the CPU. It runs at an average temp of 30 C. Justin
Feel free to email me at:
beckham@mailbox.orst.edu