ian,
i don't own Ajamsonic
i love my Audya too
so much that I own 2 Audya's

it is the BEST arranger FOR ME, for my music
sounds great through my PA, so real, so punchy, loving it !!!
Two Audya's...how cool is that?

Lee, if I gigged as often as I did several years ago, I quite likely would have
two Tyros4's...one set up at home, and one in the gig bag ready for the job. I could prepare stuff on the "at home" instrument, and load it in the 2nd keyboard via flash-drive at the venue.
Right now, one is plenty. Like you, I feel I have the proper tool for my use...the Tyros4 is certainly not the "perfect" arranger, but it is closer to being perfect for my needs than any other type, regardless of model or brand.
Like Marty above, I do not activate SA with foot-switches...I use the buttons, and assign one pedal for sustain, and the other is a Yamaha FC-7 Volume pedal, the latter being indispensable for more control over RH voice expression. I find I get enough control over SA/SA2 voices with playing technique and/or the wheels, as well as the buttons.
I also use the sustain pedal with my
left foot as I find my right foot is best for using the volume pedal...too many years on organs to break the habit.
Do you use a volume pedal, or, more accurately, what pedals do you use and how are they assigned?
Are both your Audya keyboard versions? Have you considered adding Ajamsonic?
Ian
PS...I like this little showcase by Marty as well...nice subtle use of the T4's vocoder at the beginning. He is a very talented player who would sound great on any brand or model of arranger keyboard.
http://www.youtube.com/watch?v=xztUzUKEVnk