With the newest software, based on the code, you should be able to run A4, A6, A721 and A741 with the same raspberry pi.
on the same daisy chain at the same time?
pi >>>>>>> 721 >>>>>>>721 >>>>>>> 741
would be nice to see them say this.
I would be annoyed further to find I can not do the chain above.
Frankly I guess I am just in a crappy mood today so rather then post I will sign off here.