viken- First of all I agree with you- lets start from the beginning.
Take it one step at a time. But before we begin know that you don't need to throw your money at this buying all sorts of other software and more hardware and hope something will magically work. You have all you need now.
So, the first step is to forget the secondary monitor right now and let's get the computer screen preview working in 3D.
When you launch Vegas Pro* you want to first go into your File / Properties and set the Stereoscopic section to anaglyph red / cyan. Don't question this, just do it as I instruct!
*Be sure your timeline is blank. If not, go to file / close and get rid of any remnant prior project you have been playing around with.
Now go to your explorer window and navigate to a folder that has a known 3D MVC
file. You should have imported this from your Sony TD10 using PMB software so that the file looks like a bunchofnumbers.m2ts. If you are not using m2ts file from the TD10 as imported using PMB, go now to your TD10 and connect the USB line and open PMB and import a good 3D video clip. OK, now with the mouse, drag that file from the explorer folder window to the timeline window in Vegas and you should notice several timelines get automatically created depending on the file type audio you shot with the TD10. I have my file / properties Video set to HD 1080- 60i and 5.1 surround in the audio tab so I can import that file size to my Vegas timeline. If the file was only 2.0 stereo that's OK as those properties settings will default to 2.0 anyway. Note that when you select anaglyph red / cyan the top setting will auto correct itself to custom 1080 x 1920 60i as I recall from memory. Don't worry about this as it is automatic for 3D anaglyph. Important reminder to select 3D stereographic setting to anaglyph red / cyan. Note this setting has nothing to do with your render output. It just tells Vegas you'll be editing in 3D mode and you'll be able to quickly detect if the video you added to the timeline is indeed 3D in the Preview window.
Now click and drag the 3D file to the timeline and put the viewing cursor somewhere in that clip. Your preview window should show the anaglyph form. If not, you need to do the following: ( think this is where you are having trouble)
Right click on the preview window somewhere in the 2D image. You'll get a menu at the bottom of it will be an item that says Video Preview Preferences. Select that and set the Stereographic 3D mode to "USE Project settings" or anaglyph red / cyan. If you want to understand what the purpose of the other settings are you can learn these in the help files. But I recognize that you already read those help files so you already know what they do right?
Please understand that the setting you select for your preview monitor has absolutely nothing to do with how your render will output.
By now you should be seeing an anaglyph of your 3D file in the preview monitor if you followed what I instructed.
This is where you wanted to be and achieve so you could edit your 3D videos and I hope this gets you to that point. If not then we need to go through each step and do the detective work to determine where in the process you failed to do as told. In the past the most common mistake students have made with this is 1. not reading my instructions and deviating from the procedure I outlined 2. Failing to import the right file from the TD10 either by not following the instructions or taking shortcuts and just importing a 2D file they thought was 3D.
IF you get this part resolved, the next step will be to get your secondary monitor working. That can get complicated as the process is different depending on your monitor and card. To be honest, you may need to contact forum member John Shultz as he has the Quadro card and knows that, as I don't. I use an 8800GT Nvidia card and can help people get that set up properly. To preview the process, you'll need to first properly connect the monitor to the right card output. Next you'll need to set the computer for dual monitors and set the secondary for 3D. Third, you'll need to set the secondary 3D monitor preferences properly in Vegas which can get tricky and is mostly dependent on the monitor compatibility with your card. You'll likely be doing a lot of trial and error settings in the Vegas setup part but once you figure it out you'll be able to set it and forget it. Once set seeing the video in 3D on the secondary monitor is just a matter of clicking on the secondary monitor button. Now you'll have both preview and secondary working. What I do then is reset the preview monitor from anaglyph to left eye only and use the preview for 2D viewing for editing. That is just my preference since looking at the secondary monitor I'm wearing polar glasses and if I left the preview in anaglyph, I'd be swapping glasses all the time.