That depends on what AV AMP, BDP, and projector you're using. If the AV AMP has better video processing chip than the BDP and the projector, it is better to go thru the AMP to the projector, and then set it to perform most of the video processing there. Although BD movies are usually 1080p24, but BD concerts are sometimes 1080i. You need a good processing chip to do de-interlacing (meaning convert it to 1080p) before the video signal can be sent to the projector's display panel. Moreover, a good processing chip will produce far better image when you playback DVD, which requires heavy video processing such as up-scaling, de-interlacing, noise reduction functions, ... etc. Many (low priced) BDP and even projectors cannot handle it very well.
Put in simple words - you must try it before you can conclude; but you can have an educated guess based on the video processing spec. of the equipment in the signal chain (BDP, AV AMP, and projector).