Connecting at AMS - Bus Gate A9
...and reporting back.
A9 is indeed an "external" gate where the bus stops on the tarmac, with an escalator leading up to a walkaway to the gates. This is annoying and does add on some time to the connection. I did make my connection, timing as follows:
Landed on Thursday at 09:20 (on few minutes early)
10 minutes of taxiing
15 minutes to disemabark, including waiting for the bus, until arrival "gate" A9
10 minutes to get through the terminal to E17, including security (security was empty, and the ten minutes include light jogging...)
.