First, X Modules are not the same as kernel modules. I have glx loaded in my X.Org but yet it won't appear under lsmod. However, some modules load both a kernel module and an X module (e.g. nvidia normally appears in both lists).
So the fact that int10 isn't in lsmod means nothing.
Unless there are errors in the X log, chances are int10 is loading just fine and therefore you'd expect tv-out to work.
However, having slamd64 may add to the problem. Not everything has been converted to 64-bit code properly and some stuff stops working properly, especially older modules that haven't been updated.
You would probably need to make sure all this stuff has been compiled properly for x64. That's a big job.
After all that, it could also be a million and one other things - the nvidia drivers may not support it for your chipset, you may not have the latest version, you may not have the latest int10 module or X.org etc., it may be displaying NTSC instead of PAL ( Option "TVStandard" "PAL-N"), etc. The list could go on forever but pretty much all of them are related to X rather than consoles.
When you say scrambled, I assume you mean like a random blob of memory is displaying on the screen. I have nVidia cards with TV-Out and when I was reading up on them when I first bought them, I read that this was a known problem with switching to text mode and there was nothing you could do to make them work properly. My cards are old, however, and the drivers have been updated many times since.
This also seems quite relevant (from the nVidia README):
"The NVIDIA X driver may not restore the console correctly with XFree86 versions older than 4.3 when the console is a TV. This is due to binary incompatibilities between XFree86 int10 modules. If you use a TV as your console it is recommended that you upgrade to XFree86 4.3 or later."
The only other mention I could find (during a quick google) of int10 in nvidia drivers was
Option "UseInt10Module" "boolean"
Enable use of the X Int10 module to soft-boot all secondary cards, rather than POSTing the cards through the NVIDIA kernel module. Default: off (POSTing is done through the NVIDIA kernel module).
Which I suppose you could try enabling but it doesn't sound anything like something that would fix your problem.
You could also try
http://sourceforge.net/projects/nv-tv-out/
The only other suggestion I have is to go find nVidia's website and ask them instead. This is the price you pay for binary drivers
