Windows 7 does not have a built-in MKV splitter and Haali splitter is know to be very buggy on Win7, crashing about 1,500 times a day according to Microsoft.
You don't really need CoreAVC since the MS Win7 decoder can use DXVA decoding for far lower CPU usage than any CPU only software decoder.
The catch is, MS Win7 decoder is know to be buggy, even in the RTM release. Doom9 forums has plenty of horror stories about it. MPC-HC's DXVA decoder is far more reliable, but doesn't support VC-1 interlaced files, only progressive. MPC-HC's H.264 DXVA works great though for both progressive and interlaced.
There's also other limitations in MS Win7 decoders, you'll find out pretty quickly.