Mac Pro audio for FCPX I have been using an elderly iMac for FCPX and finally made the move to the new Mac Pro. However, the Mac Pro has pretty lame audio output, so I'm looking for a relatively inexpensive solution that can give me equal or better audio compared to the iMac.

I have two fairly decent unpowered 8ohm speakers that I could add a subwoofer to for 2.1 audio monitoring.  Does anyone have suggestions for an amplifier that might take mini toslink jack input? I would like to keep the budget as low as possible.
Since the speakers are un-powered you will certainly need either an amplifier or a receiver that can handle the Toslink.  Honestly, if you are trying to keep the cost as low as possible, you may have more luck buying new speakers that take digital input.  

Toslink input on a receiver is a mid-range feature if not a high end one, so you probably aren't going to find a lot of cheap amps with it and depending on how good the speakers are, it might not cost that much to replace them with a purpose built system. (For example, Behringer makes this set.)

Alternately, you could go with a simple analog amp.  Toslink itself is more consumer targeted and probably isn't going to give you that huge of an advantage over an analog output unless the DAC in the MacPro is really poor, though even if it is, when you are working on a budget, you probably aren't going to get a substantially better DAC, so investing instead in a basic clean analog amp might get better overall results.