I'm guessing that that little amp will be a weak spot.  I would have gone for a better amp for the P4's.  Or just bought the A2's (with a subwoofer) or for the A5's (no subwoofer needed though you can use one if you want) which already have built in amps.  The amps in the A2's and A5's are obviously custom matched for their speakers, have cleaner power, and are higher quality than the Lepia.

Have you listened to the AudioEngine speakers?  You have nothing to worry about in the lower midrange, the A's are great there.  The 2's have very good bass considering their size but I like them a LOT when paired with a good subwoofer.

Since you spend hours per day on the computer, spending a little more, if you can justify/afford it, will pay off in enjoyment for years to come.

probably better.  can also consider the N22 by AudioEngine which is essentially made for the P4's.  30 day free home audition too