Agree that there's no downside to using a TA (of course, I'm biased). A TA who makes a lot of bookings with Aman and develops relationships with the team of Aman GM's is a valuable resource for you. Just this morning, I was able to get an offer of an Amandari upgrade from Valley -> Pool prior to booking. Other TA's on FlyerTalk can doubtless do the the same for you.

However, you won't get an upgrade into the Kilsari Suite at time of booking. That's a one of two specialty suites at Amankila, and the resort is not going to give up the opportunity to sell that suite. That's just the reality of things.

You might ask about upselling at time of check-in ... the worst that can happen is they'll say "no."