Only if you actually want a mainstream candidate does a vote for another mainstream candidate actually harm your chances. You could vote to approve of every candidate except the two mainstreamers. You could vote for nobody BUT the outsider candidate you want.
Approval doesn't just give you leeway in choosing who you want, but also who you don't because in this system you choose or not choose each candidate separately.
Here's the thing though: If you simply check the box next to each candidate you like, you're just a lot more likely to get one of the ones you liked. It won't leave ~49% of the voters feeling burned for 4 years, which will lead to fewer crazy people. Which won't really help me convince Dok Howl, but...
I'm just curious as to what I said that led you to infer that.
No idea, in fairness. I guess just the way you seem pretty sour about democracy in general.
As far as IRV goes:
http://minguo.info/election_methods/irv/IRV is very good at preventing minor parties from interfering with the two-party system, but it is arguably no better than our current plurality system at expanding the two-party system and giving other parties a chance to actually win elections. Furthermore, if a third party ever does become strong enough under IRV to seriously threaten the two major parties, they could hurt their own cause and wreak havoc with our entire political system, just as they could under our current plurality system.
So yeah, IRV is more of a Dok Howl pick.