Hi,
There is no such thing like "our filter".
We are not using any "filter" extensions.
The filter design you see in the Asymmetric DEMO, is visual only. In the background it is still using the Virtuemart sorting. We just designed the elements (mostly with CSS) and made them nice and user-friendly.
So, if anything doesn't work with Official Virturmart, then it won't work with Asymmetric as well.
Regards,
Support