These kind of extender/riser cables should work and can help to circumvent the bracket/space constraints. You need to check all the pins/soldering points, though. The one I bought had one soldering pin bend over to its neightbor, which could have caused some kind of short circuit. I noticed it in time and just soldered the pin to its correct soldering point. Did some quick tests with HDSP Madi and AES, which both seemed to work without issues.
I also bought one of these ASMedia based cheap adapter cards, but it does *not* work at all. It's worth mentioning that mine comes with those small onboard condensers that almost look like resistors. It looks similar but not the same as the main image shown in the following Ebay link. The Startech one and the later images of the same Ebay link show big black condensers.
http://www.ebay.de/itm/Internal-PCI-E-S … 281594e06b
Concerning the power requirements: The non working riser adapter needs to be plugged into the 4-pin power plug in order to power any card. On the other hand I also own another adapter that connects its internal PCIe card to an internal/external riser/adapter with two PCI slots. And while this also offers external power via SATA power plug it doesn't need any external power to power two RME cards at the same time (PCIe provides enough power on its own).
http://www.ebay.de/itm/PCI-E-express-X1 … 4ad409662c