I have several SACDs and have M60s, VP150, QS8, and Hsu VTF-3R. Keep in mind you generally can't hear over 20Khz. If you're over 30 you probably can't hear that high.
I my opinion the advantage of SACDs isn't the higher sample rate, but the higher quality mixing and mastering in the production. Even this varies from album to album, based on the recording and mixing engineers, production facilities, etc.
I have several DVD-A albums and the Digital Dolby 5.1 track sounds as good as SACD, despite a much lower sample rate (which is still far above 44khz-sampled CDs).
If the SACD is multichannel surround (some are stero only), that's often a big source of improvment, if the surround is intelligently and tastefully done.
My advice is you don't need super tweeters -- your M80s are already super enough!!
If you don't already have them, get some Axiom QS8 surrounds, a VP150 center, and a good sub like the EP350 or higher. THOSE will make a difference you'll hear.
