Hi there. I'm a local who's interested in the band scene here. Well, there are venues for original music here, but they remain somehow underground, so you have to knock on the right door to find 'em. For a start, you may want to check out HK Underground's site
http://www.undergroundhk.com
It's pretty cool! The shows are often held in clubs in Central/LKF and there are indeed a lot of foreign/expat musicians playing here. (check underground past to see how the shows looked like...I played in one of the gig too)
For the other venues you need to know the right people, cuz it's pretty much a small scene that celebrates itself and is (as of now) 95% local.