Best place that I can recommend is:
Home Theatre Pro Shop
2/F Grancastle Commercial Centre
2T Sai Yeung Choi Street South,
Mong Kok.
ph 2388 9394
We purchased our Sanyo PLV-Z5 Home cinema projector from there, and they have one of the best demonstration rooms in HK for projectors. They have some very serious gear in there, I saw a a topline Marantz DLP and a Runco in their demo rack, so they cater for all budgets.
Their demo room is very quiet, properly blacked out etc.. At a guess I'd say their room was 80m2 - 100m2 ?...
Its not your typical department store deal, as its located in a building you'd never expect to find such a shop, but its very much the same style of high end hifi/av shop I am used to buying my gear from back home...
You should be very happy with what you find there...
Hope that helps... Here are some photo's of our modest home cinema at home, just for good measure. I'm running progressive component output from our DVD player into the Sanyo, and its as sharp as a tack. Absolutely love this projector, natural black level, exceptional shadow detail that shames our plasma, every bit as good as all the reviews I read online, prior to buying it.