Hi
I believe Vixen software is MIDI based which is another way to sequence lights as far as I know Vixen does send out TTL I have no experience with it and you may want to hit the vixen user forums for more information on Plugins that work on available interface boards for it.
Now for TTL and how to wire it TTL is either on or off its voltage a maximum output between 3.3 and 5VDC that comes off of a digital to analog converter DAC in most cases 8 channels per board, these would be wired to the relays on you lights and sounds of Christmas.
There are most likely DAC boards that interface with your USB port on your computer that are compatible with Vixen software you would need to consult with the support forums that are on the Vixen website.
Remember TTL is on or off no fading which does limit what you can do with your lights. The lights and sounds of Christmas is on or off no fading in and out of lights. DMX would be a much better way to go you would use a Vixen compatible board and an analog to DMX converter to DMX dimmer packs that would drive your lights.
Analog allows you to go from 0 to 5vdc which will in turn bring a dimmer up and down allowing lights to fade in and out. you could use a combination of both analog and ttl to get more control outputs to your lights some would fade and others would turn on and off.
Here is a link to a forum discussing Vixen and TTL you may want to jump in on that one.
http://www.efx-tek.com/php/smf/index.php?topic=1934.0
We are laser light show heads here on photonlexicon the stuff we do is a lot more expensive, not that what you are trying to do is cheap.
But If you get the Laser bug look out its kind of like the saying for any one who owns a boat "break out another thousand".
Hope this helps
Good Luck
th