I have done this on and off with my 3805,... I did not really see an improvement in headroom or anything else, on the other hand I did not see any loss of performance either
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One thing it will do is allow a little more flexibility in your set-up. eg: I bumped the 12" woofers in my mains by +4, so that was kind of fun to listen to music and movies (for a while). So if you have a tricky room, or speakers that lack a little midrange punch, lack a little bass etc. you can give it a little boost (or cut back a little) relative to the other half of your speakers
