D-Link has released the first firmware update for their DSM-750 Extender.  Based on the release notes it appears that most if not all fixes in the new version 1.01 apply to the MediaLounge software and not the Media Center Extender aspect of the product.  That said it does appear to add 1080p output as an option which should apply to both the Extender and MediaLounge modes.

You can directly download latest firmware or simply upgrade via the front USB port on the DSM-750.