I don’t suppose anyone here might have come across such a problem and have an idea of how to fix it?

just for the records, I paste here my final .asoundrc, using
dmix, alsaequal and 96k upsampling. It took me some time to get to
this point, and enjoy Spotify like never before. alsaequal is just genius!
This also contains the ‘Skype trick’, that fixes the ‘warped voice’ issue under Kubuntu 64.

fbx

# —— Let’s set the good converter as a default
# —— Moreover, it seems that the rate_converter option inside the plugs does not work

defaults.pcm.rate_converter “samplerate_best”

# —— Let’s use dmix as our main playback device,
# —— and make sure that it opens the device at 96k
# —— This also sets the device at 96k, visible in /proc/asound/….

pcm.dmixed {
ipc_key 1025
type dmix
slave {
pcm “hw:0,0″
format S32_LE
rate 96000
}
}

# —— The Skype magic, to make it work under x86_64, avoid the ‘warped voice’ problem
# —— Never understood why it does not work without this thing

#one called “dsnooped” for capturing
pcm.dsnooped {
ipc_key 1027
type dsnoop
slave {
pcm “hw:0,0″
rate 96000
}
}

#and this is the real magic
pcm.asymed {
type asym
playback.pcm “dmixed”
capture.pcm “dsnooped”
}

# Final pcm device, for aoss or for normal apps, like skype
pcm.dsp0 {
type plug
slave.pcm “asymed”

# A hint is required for listing the device in some GUIs, e.g. Phonon configuration (KDE).
hint {
show on
description “My asymed plug device”
}

}

ctl.mixer0 {
type hw
card 0
}

# ——— End of the Skype magic

# ——– My audiophile equalizing section

# a small intermediate plug that points to the dmixed one
# Never understood why nothing works without this
pcm.postequal {
type plug
slave.pcm “dmixed”

}

# to control the equalizer with alsamixer -D equal
ctl.equal {
type equal;
}

# a plug that equalizes
pcm.equal {
type equal
slave.pcm “postequal”
}

# a plug that upsamples everything at 96k before equalizing
# so that we make the equalizer work always at 96k, much better sounding
pcm.upequal {
type plug
slave {
pcm “equal”
rate 96000
}
# Alsa chokes if this is uncommented… bug in alsa?
# Anyway the good converter was set as default
#rate_converter “samplerate_best”

# A hint is required for listing the device in some GUIs, e.g. Phonon configuration (KDE).
hint {
show on
description “My upsampling equalized plug device”
}

}

# ——— And now the ALSA default devices. Spotify wants these, at
# ——— the end we’ll have an upsampled, equalized Spotify listening experience
# ——— Any other player will work through these as well

pcm.!default {
type plug;
slave {
pcm “equal”
rate 96000
}
# Alsa chokes if this is uncommented… bug in alsa?
# Anyway the good converter was set as default
#rate_converter “samplerate_best”
}

ctl.!default {
type hw
card 0
}

ALSA Application Mixer:
http://forum.dug.net.pl/viewtopic.php?id=17368

After setting everything up and setting the Alsa output device in ~/.moc/config to “equal” I have what I’ve wanted forever.