low sound quality using dmix

[SPU]

Kubuntu 9.04 amd64
(libasound2 1.0.18-1ubuntu9)

I have E-MU 0404 USB locked to the 44100 on hardware level (but my problem isn't frequency dependent). This card has no hardware mixer, so I'm trying to get "working" software mixer, but with no luck.

The problem:
When I start aplay with default device or "emu" (see my config below) I have a clean sound like it must be (but no software mixing), when I use aplay with "emutest" device I have a noisy sound like it was in 8 bit.
May be dmix doesn't support S24_3LE output format which is only supported by current driver for my card and falls back to 8 bit format? But I don't get any warnings about unsupported format:

> aplay -D emutest /tmp/test.wav
Playing WAVE '/tmp/test.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo

hw_params:

access: MMAP_INTERLEAVED
format: S24_3LE
subformat: STD
channels: 2
rate: 44100 (44100/1)
period_size: 5513
buffer_size: 22050

My asound.conf:

pcm.emutest{
 type plug
 slave.pcm "emudmix"
}

pcm.emudmix {
 type dmix
 ipc_key 1234
 ipc_key_add_uid false
 ipc_perm 0666
 slave {
 pcm "hw:0,0"
 rate 44100
 period_size 5513
 buffer_size 22050
 }
 bindings {
            0 0
            1 1
        }
}

pcm.emu {
 type plug
 slave {
 pcm "hw:0"
 rate 44100
 }
}

pcm.!default {
 type plug
 slave.pcm hw
}

ctl.!default {
 type hw
 card 0
}

[SPU (spbamdclub)]

Duplicate of https://bugs.launchpad.net/ubuntu/+source/alsa-plugins/+bug/375993 (reported twice because of network failure)