This might be more ambitious than your friend want to undertake, but you can try this site:
Here is a comparison of several different drivers in different alignments.
When looking at any woofer spec's, ALWAYS take a look at the impedance at resonance. The higher the impedance, the more "out of control", "bloated" or "one-notey" it will sound. While this is not nearly as critical for HT use as it is for reproducing music, it is something to consider. If your interested as to why this occurs, let me know and i'll do my best to explain it in "English". Sean