Mastering for iTunes: compressed sounding files!

Hi...I'm mastering my songs for iTunes by using the droplet (of course).

I have followed all of the advice out there about making sure the files i drop aren't too hot in order to avoid the sound of compressed files.

Nonetheless, the files resulting from the droplet not only sound compressed, they are not nearly as loud as other files Iahve purchased on iTunes.

So there is both a volume drop when one of these files plays, and after multiple instruments enter, the lone instrument that was playing before loses its presence due to compression.

These are aiff files, and again, when I recorded them in real time, they were well below the peak threshold.

What am i doing wrong?

Please help....Thanks