Not sure what kind of board Asus is using for this A8 APU, and not sure how the 7560D behaves in the presence of a discrete card. In H77/87 chipsets, the HD 4000/4600 integrated graphics are disabled and in Z77/87 chipsets, the integrated graphics are enabled, but not sure how FM2 manages its graphics. Maybe Radeon -G graphics don't like Nvidia?
Anyways, the 750 Ti is a fine choice, and you could also wait for the R7 265 to get a little more oomph and overclockability, but you really need to invest in a better PSU. If it were a 350W seasonic 80+ gold PSU, it might work, but it's clearly not. Bookmark this guide for reference
http://www.eggxpert.com/forums/thread/323050.aspx
NO, NO, NO. Whoever told you that bigger is always better needs to go back to square one for learning about PSUs. You need what you need. 100w more than that is being safe, 200w more than that is futureproofing for SLI/CFX, 300w is overkill and a complete waste of electricity and money. For God's sake guys, this is an AMD APU PC and the 750 Ti doesn't even draw more than 75W.
@Bad_Kitty13 yes i must agree with your point about XFX PSUs; all of XFX's power supplies are made by Seasonic and you can't go wrong with them.