i'm a little confused (what else is new?).

by rear surrounds, i imagine you mean back surround and not surround.

this would limit your sources to DD-EX, DTS-ES and matrixed modes, as multi-channel audio only discs don't use these channels at all.

in any case, the general rule for selecting amplifier power is to use an amp that can deliver twice the power of the speaker's continuous power rating, or, 3 db headroom. in critical listening environments, the recommendation is for 6 db (4 times the speaker's cont. power rating) headroom.

this headroom is to insure that transient peaks are delivered to the speaker cleanly...no distortion. distortion (the amp into clip kind) is what kills speakers and can be damaging at surprisingly low power.

unless you have clip indicators on all of your amps and you watch them instead of the movie, you mostly won't know when the amps clip during a transient peak.

all of this means that if your speaker is rated at 100 watts, continuous, you should use an amp of 200-400 watts. this is playing it safe and is the main reason that higher power amps sound better (assuming specs that are real).

also to consider is the speaker's sensitivity. as i recall, soundhound uses horns that have extremely high sensitivity. this means that they require little power to acheive reference level (like, only a few watts) so 40-60 watt amps means he has gobs of amp headroom. my speakers require 10 times the power of soundhound's to reach ref level.