To answer you question, I say why don't you try it? there's nothing to loose and it just might run.
But I will probably be unstable.
I highly recommend upgrading to say X3 or even better X3 Studio. X3 Pro might be overkill for you if you've been happy with HS 6.
To bad you interface has no XP drivers but this is true all new interfaces coming out. Good news is you don't need an interface to run HS 6 and open and re save the projects properly using the old XP computer.
I have a feeling HS 6 did not have the per project option mentioned above. But you can accomplish the same thing buy creating folders for each song using Windows Explorer. Then performing a "save as" and point the project to the folder you made.
Be sure and check the:
" Copy all audio with project" box. This will give you a folder for each song with all the needed data inside.
Important-
Save the projects as Normal- CWP files,
do not use Bundle - CWB Bundle files are known to behave as you are describing.
I know this works because I have opened a few CWP files I created with HS 5 back in 2004 and it worked just fine on X3. Only issue was a missing reverb plug in.
One other item that will cause Sonar to not load an audio file is when the clock rate is different.
Make sure the clock rate of your new interface matches the old one.