Welcome to SPCR!
Any proper case with sound insulation and less gaping holes
in it should beat the 900 sound wise. The SPCR Recommended List
are the first places to start your search. The 900 is a 47-48 litre case with a price tag of roughly 120 EUR, so going by that I'd start the search at the SPCR Recommended Fractal Design R3
, now superceded by the R4. Might find an R3 on clearance sale if you're lucky.
The R line of cases has modular airpaths, solid construction and sufficient cable management. The Corsair Obsidian 550D is another SPCR Recommended case, if their looks are more to your taste, but it has some HDD vibration issues AFAIK. The 650D has a hole in the side in the form of a window, not really a good thing for silence.
You should mention your CPU cooler, video card and HDD makes and models so people can give their opinion on whether replacing those might be a better investment than a new case. Silent parts make the silent PC, the case is just icing on the cake.
PS. I noticed you're using the stock CPU cooler. That should be the first item on the list before you start looking for a case, if you ask me. Stock/reference coolers are usually pretty terrible from a silence perspective.
PPS. Easy first aid is just leaving the LEDs unplugged (from mobo). No need to maim the case!
PPPS. What's your case fan setup? Besides coolers, fans are probably the second biggest noise source in the average case with no prior silencing effort.