1% distortion is several orders below being audible in subbass. Impedence rise won't necessarily save you all the time, it's not some type of catch all throw as much power on it as you want type of phenomenon. I think that's the impression many are getting, since honestly, only a handful of people on this forum knew what imp. rise as of 6 months ago. I rarely heard it mentioned except in rare instances followed by "whats that" from a random member. (not bashing you, just saying it's being thrown around a bit much, IMO) Regardless, even with imp rise, he's getting more than 1000 watts out of that amp, the extra power, even with imp rise is likely to not be noticeable. Let alone with the extra chance of damaging the driver if he gets a short moment of slight stupidity. However, like I already said, if he sees himself upgrading, he might as well get something bigger, if his electrical can handle it.