What's a reasonable listening position response curve?

I think Dirac uses +2/-2 from 30 Hz to 20 kHz, take a look at this thread...

There's the Bob Katz method flat to 1khz then linear diagonal to Nyquist which makes it about -7db 20khz. Some like a bit of bass boost but you need to watch your headroom. You could Google Harman curve for some info on that method.

Human beings can hear 0.1dB so the maximum tolerable variance is at most +/- 0.05dB, and I would go .01 just to be sure. Remember, sound quality is 110% entirely determined by frequency response. It is totally worth whatever EQ it takes to get this dialed in. EQ circuits do not alter sound in any way other than to make it perfect.