ASUS P8B75-V for the slightly better quality over the pro4/MVP, being an Asus board and all. but if you want to cheap out, feel free to go with the latter, or any of the matx board if all you're adding is a sound card and a GPU.
case in point; you're not going to see a whole lot of difference performance-wise between the boards. focus on build quality, price and feature sets (no. of usb3.0's, PCI/PCIe slots, etc.) that are to your liking.
I am also little bit inclined towards ASUS P8B75-V but in comparison to ASRock H77 pro4/MVP, ASUS P8B75-V do not have the HDMI Ports and it is B75 chipset. Even the Audio I/O Channels are better in pro4/MVP. Could you please tell me how B75 chipset is in comparison to H77 and how much HDMI ports matter in real life.
For ASRock H77 pro4/MVP I am not sure about its Multi GPU support and its memory frequency is 1600 MHz compare to Asus 2200(O.C) MHz. (although i do not have a any clue about what are these
And if in the end I have to chose from the other cheaper two, i.e., ASUS P8B75-M LX and Gigabyte GA-B75M-D3H then which one shall I opt for.