Error 80070057 with surround audio.

[TTH]

I receive this error when I try to play 5.1 MLP files or normal stereo files mixed to 7.1 (in_dshow+FFDShow) through DirectSound Output:

"Error creating DirectSound buffer.
Error code: 800750057"

Stereo works OK with any plugin.
ASIO output plugin doesn't have problems with surround, but it prevents other applications from playing any sound.
OpenAL output works as well, but it mixes surround back to stereo (probably that's because I use Vista).

I'm using Vista Enterprise x64 and ALC889A HD Audio.

How can I fix this problem?