Sorry,
Have been busy with a lot of other things lately (new job, buying a house for around the new speakers

)
I have build a test enclosure containing 60 liters, being designed for a closed box with a Qtc=0,57 .
The enclosure is not perfect (has bracings, but is made from 22 mm MDF). But for initial testing it is suitable.
At first: the unit takes a long time before breaking in. In the beginning you really notice a low sensitivity and you need to crank the gain up. But already after a week (24/7) playing with ground deep slamming basses, the unit becomes more loose! And you can really notice that!
After two weeks I have done some serious listening and the results were pretty satisfying. I've put the XO at 150HZ and it blended very easily with my current speakers and also with those of a cousin (large Seas EX4 speakers). At his place we had a Metal meeting, with a lot of spoiled audiophiles listening to Metal and the sub was foudn to be excellent, fast, deep and musical
Contrabasses can be followed very easily (even when you disconnect the main speakers), you can hear perfectly the characteristics of bass guitars etc.
They are worth the price!
At this moment my cousin is running in the other unit in a BR enclosure (way too small, about 30 liters) not designed for this unit. In HT the bass is slamming deep though! Promising I would say.
Later on, I will try to do some tests with special equipment to fine-tune the enclosure and after that I will start building the final speakers.
I will keep you informed!