If you could possibly consider pre-owned stuff, try to find an AVR for around 7K-8K and then try to work out with DIY Master about a possible 12K-13K set of speakers. I think you wont be able to include a subwoofer muna for that amount, so sa next ipon nalang yon. Gamitin mo muna ang fronts for LFE tutal tight naman ang 9 sqm na space. Or perhaps get 3 speakers (2 fronts + subwoofer) muna. I think that would sound fuller than most HTIBs. Hindi mo nga kailangan ang loud because of your room size, but you would still want a fuller sound kahit hindi mo malakas ang volume dahil sa kabitbahay - nagagalit ba kapitbahay sa ingay?
Problem with spending good money on an HTIB, you might end wanting to upgrade to a full size HT soon. In that case, mapapamahal ka lang lalo. So I would suggest na kahit hindi mo makumpleto agad ang full 5.1 system within 20K, then paisa-isa nalang muna.
Kung masikip ang room, maganda rin sanang combination ang sound bar + rack type subwoofer. Tamang-tama sa 9sqm yon. Kaso aabutin ka rin ng over 20K kung isasama mo yung amplifier.