It occurred to me that Steffen Beyer wrote in gmane.os.netbsd.general:
> Hello world,
[.. ]

> NetBSD detects two uaudio devices, everything seems fine so far. But when
> starting a player, the program gets stuck and no sound is to be heard.
>
>
> Some more details:
>
> dmesg snippet:

I think you didn't give enough data.

> ehci0: *** WARNING: opening low/full speed device, this may not work yet.

There you have it; apperently your USB audio device is an USB 1.1 device,
and you're attaching it to an USB 2.0 hub. As far as I know, this is only
partially supported - the code to use the so-called Transaction Translator 
inside a USB 2.0 hub knows only how to deal with a few transaction types,
and to my best knowledge this does *not* include isochronous data, which
is the likely kind of transfers an audio device will do.

Using an USB2 hub to connect with an USB 1.1 device will most likely only
work for mass storage and some input devices. I would suggest to connect it
to a port on a root hub (in other words: Directly to your computer, not using
a hub), as this would be a different situation (The companion host controller
would take over, and normality would be restored)

> uaudio0 at uhub1 port 1 configuration 1 interface 1: ESI U46DJ, rev 1.00/1.00, addr 4
> uaudio0: audio rev 1.00

However, "uhub1" sounds a bit fishy to me. In my experience, the root hub
companion ports of a USB 2 controller get probed first, followed by the USB2 
root hub. My typical 5-port USB 2 controller  probes as two OHCI controllers
and one EHCI controller with companion controllers. uhub0 and 1 connect to
the companion controllers, uhub2 is the EHCI controller. Any external hub
would've been uhub3.

It almost seems like the companion controllers don't get recognised properly.
You didn't disable them in your kernel config, did you?

-- 
    Martijn van Buul - pino@dohd.org - http://www.stack.nl/~martijnb/
	 Geek code: G--  - Visit OuterSpace: mud.stack.nl 3333
 The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' (I found it!) but 'That's funny ...' Isaac Asimov