Hi Jan,
Thanks for such a detailed reply - I've made sure all sliders are set to 75%-100% (except the air conditioning system which I've kept at about 25%), and I've done 3 flights since my last post - the last 2 flights with XPRealistic Pro disabled, and I also set minimums to 0 for all 3 flights. EDIT: I also flew non-ILS approaches on all 3 flights.
I got the same results every time: I did NOT hear the callouts: 2500 - 400 - 300 - 200, but I heard all of the other ones extremely clearly and loudly, which makes me think that the missing callouts are just not being played for some reason.
I'm a bit out of ideas at this stage! I'm not sure why this is happening on my end - the plane and the simulator are both running the latest versions and I'm not running any other mods which might affect the sound files/triggers.
It's always possible that I'm hitting some kind of limit on the number of sounds to play, but I'm not missing any sounds on any of the other planes which I fly (Zibo 738, Rotate MD80, Carenado Citation II, C172 and Beechcraft Baron) - very strange
Thanks anyway for your help - this is something I can live with if we can't pinpoint a fix, it would just be great to resolve it!
Cheers