I have Triton Two's as my mains. Fairly large listening area 20x20, high ceiling. Listen to 90% music. If cost is not an object which would be the best surround/rears? Aon 3's or Super Sat 3's? I heard the Aon 3's as mains through an expensive tube amp and they were WOW!

For most people the issue is form factor - if the Aon 3's "fit" as surrounds in your environment they certainly will make great surround/rear speakers. Opinions abound about whether it is important to have quasi-full range performance from surround/rear speakers in a home theater and the Aon 3 is certainly more full range than the SuperSat 3 or SuperSat 50. For most people, the advantages of "fit" will outweigh any advantage of the more full range speaker. And keep in mind, as you set your crossovers to direct bass energy from the surround/rear speakers to the subwoofer, the actual difference between the Aon and SuperSat is diminished and potentially even eliminated.

Just FYI, I use SuperSat 50's for surrounds in my system - they are an appropriate form factor and a bit more full range than the 3's. A nice compromise between these two directions. Hope this all helps, enjoy your system.

You answered the question for home theater but would the full range Aon 3's have an advantage for surround music?

Generally the same - but ... multi-channel music is a bit of a mixed bag right now - and it may depend on your feeling about what's "right", or which way things are going, regarding multi-channel music production.

If multi-channel music is mixed such that "you are on the stage with the musicians", one could make a strong argument for quasi-full range speakers (or speaker plus sub) for all channels. If multi-channel music is mixed so "you are in the audience", the typical sub/sat arrangement preferred for home theaters is fine.

Just to complete the circle, some people prefer full range speakers for every channel for movie playback, although our experience shows that the unless the room is very large (like a movie theater) the typical sub/sat arrangement actually gives the best results and allows for the most acceptable form factor for people's living spaces.

Ok if I do go with full range speakers in the rear are they then set to large? If small what crossover frequency do you recommend? My default on my Rcvr. is set at 120 Hz

No, set them to small. For Aon 3s, use a crossover.setting in the 60-80 Hz range.