I know that folks have built routers, using X86 (or other) PCs, and network cards.
I was wondering what kind of PCI (express) modem card would be required ( something like this? ... ) to do similar with OpenWrt. Or if it's even possible at all.
I assume that the nature of the beast is handled by specific chips in the VDSL modems themselves, I just wondered if those are available for builds (like the 132), or (if those are too expensive) they're emulatable (new word!) by software.
You do realize that the product in question is a full VDSL modem (running its own proprietary firmware from flash) on its own accord? It is basically an 'external' VDSL modem with the case removed and an ethernet card in PCIe form factor, your only access to it is using Draytek's webinterface.
Hot glueing any random VDSL modem to the inside of your PC case and lopping back its LAN output to your ethernet card would have exactly the same results. While there may be cases where this form factor might be beneficial, there is no functional advantage to this design - and either is far away from 'build[ing] a VDSL modem".