The plan, is to incorporate the Quad drivers and passive crossover, into a sealed chamber within a much larger cabinet, designed for a 12" Woofer. An active x-over will split the signal at around 300Hz and separate amplifiers will power the Bass Driver and the assembly from the Quads. The Quads are a 6.7L ported design, so the T&S parameters of this small midbass driver are needed, to calculate the volume of a suitable sealed chamber.
These results were measured for the two drivers.

                           A                                                    B            
Piston Dia:    83mm                                            83mm
SPL:              84.78dB 1w/1m                            84.99 1w/1m
Re:                   3.389 ohm                                    3.419 ohm
Fs:                 80.08 Hz                                        82.1 Hz
Qts:                  0.583                                             0.583
Qes:                 0.716                                             0.737
Qms:                3.154                                             2.805                          
Le:                    0.175 mH (10k)                            0.176 mH (10k)
M(ms):              6.00g                                             5.67g
Vas:                  2.707 L                                         2.718 L

A screen shot of the impedance sweep + T&S parameters for driver "A", can be seen on the next slide.

Using the figures for "A" and maintaining a Qtc of 0.707 this calculates as a Net sealed box volume of 5.8L (without filling) with an F3 of 97.1Hz. This is more than an Octave below my planed crossover frequency and with the active filter having a steep slope (24dB/Octave), this should work well. A sealed box of 4.0L will give a Qtc of 0.755 and an F3 of 97.6Hz. The higher Qtc of the smaller chamber could possibly benefit the mid range, conversely a well stuffed 4 liters will give a virtual volume of up to 4.8L,
so there is a lot of scope for maneuver with the design of the sealed chamber.