Yep, I have one. A MOTU and an issue.
 
It works as advertised on Win XP-32 bit.
 
On Win 7-64 bit it will not work thru the MAIN outputs. There seems to be a driver conflict with Win 7. The MAIN outs show up in Playback Devices as "MOTU MAIN OUTS (1 and 2)" and the Test feature makes sound but no sound is produced from Sonar or Media Player. Headphone outs work fine.
 
After installing the updated drivers for it I now get sound from the MAIN outs, however, they appear in Playback Devices as "MOTU FW USB (5 and 6)"
or else they don't even show up at all. Yet there is sound.
 
I was on the phone for an hour with MOTU but they have not been able to resolve the issue.
 
So far I believe their drivers are not fully Win 7-64 bit compatible, since it has no issues in Win XP-32 bit.
 
Steve

I run one on Win 8 64 bit with no issues, I am outputting via SPDIF tho.
 
Have you tried updating the firmware?

My driver version is 4.0.5.4199
Firmware 1.03
 

The driver listed as the current one for that interface is: v4.0.5.7483 May 1, 2013
 
The current firmware version for that interface is: 1.04 January 2, 2013
 
In addition, in the manual, it appears from the text that you may be able to control volume to different sets of outputs, by pushing in the volume knob and holding until the desired output's led lights.  Perhaps this can be used to produce sound from Mains rather than just the 5/6 pair.
 
Here is the relevant text from the manual (link to manual: http://cdn-data.motu.com/manuals/firewire-usb-audio/Audio_Express_User_Guide_Win.pdf)  - If this applies and my understanding is correct, this may explain why it is currently only producing on output pair 5/6.  (so, follow the below to get output to mains):
 
Main outs
In a standard studio configuration, the main outs
are intended for a pair of studio monitors, but they
can also be used as regular outputs for any
purpose. Their reference level is +4dB. Use the
front panel VOL knob to adjust the Main out
volume. Push the VOL knob until you see +main
LED turn red (or flash red) and then turn it to
adjust the main output volume.
 
I hope that helps.  Please note that the above manual, though the current one, appears to be from a slightly older version of the interface drivers, though I wouldn't think that would affect this piece of functionality. 
 
Bob Bone
 
 

Yes I've done all that. Remember it does work on my XP system just fine. It's only on my Win 7 laptop I have all these issues.
 
All updates are current.
 
Again, I do get sound, but there's a conflict in how Windows displays the unit in the Playback Devices window. It does not even show the SPDIF outs at all. What it does display is:
 
Plugged into a USB-2 port: 
MOTU Analog 1-2
MOTU FW USB Out (05/06)  *[This is where I get output from the MAINs]*
MOTU FW USB Out (07/08)
MOTU Phones 1-2
 
I only have one USB-2 port. The rest are USB-3 ports and the MOTU tech says there is an issue with USB-3.
 
My system may be faulty.

Thanks for the post back.
 
I understand you have your drivers installed on your laptop.  It working on XP is not relevant to your Windows 7 issues.  My listing of the drivers and firmware were more for the other individual, since his are out of date.
 
What is not clear is whether or not you have properly set the Volume Knob to point to the Mains - so that adjusting the volume knob will actually raise the volume level of the mains, which is why I included the documentation snippet.  If so, great, but I did not see that reflected in your post.
 
I did not see any complaints out on the web about this particular issue, so it is not likely an issue with the drivers, for whatever the worth.
 
Bob Bone
 

>"I did not see any complaints out on the web about this particular issue, so it is not likely an issue with the drivers, for whatever the worth."
 
Which is why my last comment was... "My system may be faulty."
 
 

I understand - at least there is output, even if it looks a little lost on its way to the mains.  :)
 
Bob Bone

Try uninstalling and using the firewire connection and reinstalling.

Also have you got any onboard sound devices? If so, disable those.
 
Also, you said you only have one USB 2.0 port. Windows can be a bit of a nightmare if over time you have connected many devices to that port.
 
So, in device manager, under "view" click on the "show hidden devices" and then manually clear out any devices that you dont use. (Do this while the MOTU is unplugged)
 
Then Plug back in the MOTU and let Windows freshly install it to your port.