That time when I wanted to use my SAFRA $100 voucher (converted to CapitaLand), I went to 'Inforcom', I think it's on level 3 or level 4 at the escalator there.
Prices are definitely more expensive, and sometimes not updated. You may want to see if they can match the prices or not (or offer it to you a little cheaper), I managed to do that once.
I bought my sound card from them. They sell quite a lot of peripherals. Not sure about cases but if I'm not wrong (but I may be!) they sell a few over there.
Best to call before going down. Google for the number yourself haha.