Drakonis,
I'm not familiar with anything about flared ports from Polk, but was wondering...how flared is flared? My point is that a simple rounding of the edges with a router isn't going to effect the tuning of the port that much. On the other hand, if the flare rate is more drastic, and extends further down the tube, I'd think it would be appropriate to treat it as a horn. Horn math is fairly accessible.
N.B.: The one thing that horn afficionados never get around to admitting is that horn loudspeaker distortion gets really, really grotesque if you go below the low frequency cutoff of the horn itself. I'm quoting from memory here, but I think the low frequency cutoff for a horn is something like
width of horn at mouth= 1/4 wavelength of cutoff frequency
This may or may not help you, as ports are usually small enough in width or diameter that it may not be appropriate to treat them as horns.
What is your goal? To reduce turbulence? Increase effiency? Extend low frequency response? (Yes, yes, yes...I know...all of the above.)
Grey