In the .6 sealed cabinet they measured well to below 100hz or so in-room. Excellent performing setup IMO when I Demo'd them in stereo with a sub to supplement the bottom end.
If you wanted to go ported, you could build the box to a tuning of down to 60hz or so but I wouldn't go much lower. That would give you a little more extension if you needed it. Dimensions etc. are kind of up to you.
I can get you however many of the custom XO's that you would need, just PM me and I will discuss pricing with you.