The mod described here outperforms the 10PR. This mod requires a more work than the 10PR. It requires cutting likely 2 round holes for ports in the rear panel, if space exists, only behind the center(s) of the active 6.5s. If the terminal boards prevent proper port siting as described (I suspect this is the case), ignore this advice unless you are wiling to move the offending terminal board(s).
The benefit is to enhance reverberant field performance. Flared port(s) centered behind the active drivers (with clear internal path from driver rear to internal flare, i.e. no damping material) output clean mid range which enhances reverberant field performance. Straight ports are fail for this purpose because their turbulence yields distorted signal.
Remove one of the active 6.5s and ship it to get the TS parameters. I suspect a DIY person with the test gear would not charge much.
Carefully calculate the cabinet effective inner volume. Input to your preferred box software the TS specs for one mid bass in one half the actual IV to get the ideal port specs and resultant box tuning frequency. Normal port length and diameter refers to a cylinder port with straight 90 degree corners.
Dual flared ports require a different length compared to a straight port. Use Precision Port's website to calculate dual flared port length (input cabinet internal volume and tuning frequency). Insure there's nothing inside the cabinet blocking the specified port.
Ideally you want one port per mid bass. Buy one Cherne plumber's "test plug" per port, to help tune around bass modes. Plug ports as needed to change box tuning and tune around bass modes. As long as you've got a foot between the rear panel and front wall this should improve performance.
If, as I suspect, those two 6.5 prefer more cabinet volume: sealing the pedestal opening for the OEM 6.5" PRs, and air tight sealing the pedestal/cabinet coupling adds this volume to the OEM volume.
You have to "trim" about 1/4" from two opposed outer edges of the inner flare to fit through its mounting hole.
