I agree with most of the others here. Your problem is the player, not the spellfire channeling. However, I also know that in some groups, getting rid of a problem player is not as easily done as said. For instance, I generally play with a gaming club at a college, and just booting someone from a club isn't as easy as getting them out of your house is.
So, if you must confront him in-game, I would first follow werk's suggestions. If that doesn't won't (and IME, it probably won't), the class to beat a spellfire channeler is a monk. The big key is getting a high reflex save and having evasion/improved evasion. After all, spellfire has a set DC of 20. In the FR game I'm in right now, my svirfneblin gnomish artificer/ranger has a Ref save of 20 and evasion, so avoiding those blasts is actually quite easy. Alternately, if the DM allows it, get a wizard to make you a command word item of antimagic field and go with the barbarian. The item in question is very expensive so you may not be able to afford it, but it shuts down a wizard/spellfire channeler exceptionally well.
So, if you must confront him in-game, I would first follow werk's suggestions. If that doesn't won't (and IME, it probably won't), the class to beat a spellfire channeler is a monk. The big key is getting a high reflex save and having evasion/improved evasion. After all, spellfire has a set DC of 20. In the FR game I'm in right now, my svirfneblin gnomish artificer/ranger has a Ref save of 20 and evasion, so avoiding those blasts is actually quite easy. Alternately, if the DM allows it, get a wizard to make you a command word item of antimagic field and go with the barbarian. The item in question is very expensive so you may not be able to afford it, but it shuts down a wizard/spellfire channeler exceptionally well.