I have my laptop DAW in the bedroom with a Line 6 USB audio interface.  I take the video from the laptop to the graphics monitor/big TV via HDMI.  When the laptop is playing ordinary music or video files or streaming from the web everything, along with the audio plays nicely through the TV's HDMI inputs.  All normal stuff up to this point.
My question/problem is this: Is there an easy way to play back SONAR projects, using the simple, line 6 UX-2 and somehow have the CW project audio become available within the HDMI signal so that ANY audio files on the laptop can be monitored through the HDMI cable only.
Sure, I could run a digital signal from the interface separately and into some mixer, receiver, pre-amp or the like and switch the audio stream from CW project audio to regular, generic audio codec to stream audio from other sources on the laptop...be it a website, iTunes or Windows Media Player and such.
To keep things simple in the bedroom there are two powered monitors and normal left and right analog audio outputs of the TV going to those audio monitors.  All audio and video from the laptop needs to run via the HDMI cable.  Naturally, to play a SONAR project, I have to use the interface with asio drivers.  How do I get asio driven sound into an HDMI pipe?  I don't see HDMI as an output in SONAR.  Why not...I wondered...
Any good ideas out there?  Yes, I could plug cans into the interface, and so far that's been my only workaround.  But I want all laptop sound to travel the one HDMI cable.  Your input is appreciated!  Thanks, Dub  
 

Well... You have a couple options. So the HDMI out is a separate device, not related to your Line 6. It is a Realtek soundcard that is part of the graphics card. So you need to switch Sonar to use that. It doesn't have ASIO by default. As such you can:
 
1) Use it in MME or Maybe WDM/KS mode.
 
2) Install ASIO4ALL and use that, it is a general purpose ASIO to WDM bridge.
 
If you want something with proper, native, ASIO support, and HDMI you'll need to buy a new unit. There is precious little on the market that does this. The MOTU HD Express and HDX-SDI will both do it, I've used them for that purpose. Expensive though, and with a laptop they need an ExpressCard port which few have. The Blackmagic Intensity Shuttle might be able to do it, haven't tested it.
 
It is kinda a pain to do pro audio with HDMI :P.

Expensive is right!  Well, thanks for the suggestions.  I've used ASIO4ALL on small projects for years but it's just not fast enough for my needs.  I'd have to raise the buffers beyond usable latency.  Even worse with MME.  Looks like I'm stuck with using cans for a while.  Thanks again.
Dub 

HDMI may always have too much latency for your needs in that case. Even pro interfaces are limited by the format. So HDMI transmits audio during the video blanking period. So it only sends audio data once every 16-42ms depending on the frame rate of the video. Audio is transmitted in packets of data, not in a continuous stream. It's all kept in sync to the signal clock and everything works out and plays smooth, but it isn't low latency, since that wasn't a design concern for HDMI. It's minimal unit of sync is a video frame, so having lower latency for the audio would not be useful.
 
This is on top of any processing, and the HDMI encoding.
 
Thus if you are after really low latency stuff, HDMI is probably not for you.

Sycraft, thanks for the HDMI lesson. I had no idea how it worked but you've explained it very well. It's kinda like sending/receiving packet data via amateur (ham) radio. Interesting.
The problem on my end is just a matter of making my late night/early morning inspirations easier to record while still in bed. I spend a lot of time reclining because of a back problem so every little bit of effort I can 'save' means more energy for me later on, when I have to be on my feet or sitting at my main DAW.
For now, I can just use headphones until I find a device that accepts coaxial digital audio and converts to analog to drive the speaker amps. My Line 6 interface has a coax output as well as balanced analog.
I appreciate all of your effort on this subject.
 
Dub

The HDMI audio is separate from the regular PC audio (e.g. RealTek or whatever).  Same way it is separate from any other audio device.  The Windows default audio playback device, when an HDMI cable is connected is the HDMI audio which is generated (in most cases) by the audio chip in the video card (some old video cards used an S/PDIF connection to the PC's motherboard to get the audio).  As Windows will only allow one default audio playback device, and as the HDMI audio is generated by the video card, I don't see any way of getting any other audio device's output to the video card.