Recently, after a system update (kubuntu maverick) I choose the option Direct hardware device without any conversions (under Settings->Configure Amarok->Playback->Sound System Configuration->Configure Phonon-> Music-> Output device) for my USB DAC, turn on my monitor speakers, started "Sometimes" by Pearl Jam and what I only can say is "ohhhh this is amazing, I never hear before this guitar!". This is what Hi-Fi men call bit-exact playback. Thank you.

Amarok, what else?

Can you provide a screenshot of this? I don't have anything named like that in KDE Trunk... it might be a ALSA device provided by your sound card, or a Kubuntu patch.

here is a snapshot:

A generic "USB Audio" has disappear (same device) and now I can choose between three options: "Direct hardware device without any conversion", "Direct hardware device with all software conversions" and "Direct sample mixing device".

That is an ALSA/Pulseaudio device, depending on if you have Pulseaudio enabled or not.

I understand. My point of view is that I've done nothing and this option is appeared, so at this time I think that kubuntu packagers have enabled Pulseaudio for me.
I'm reading now around that this features was always here in linux world, but in my case without knowing that this was possible and without this integration into KDE4 configuration, I would never have discovered this "mandatory" feature for who like listening music with PC.