I don’t have a direct answer to your question but wanted to help clear the air from previous replies that aren’t entirely correct.
Out of the box, MediaCenter allows for up-to 4 tuners of EACH TYPE. So, 4 OTA ATSC, 4 NTSC, 4 CableCARD, etc..etc.. You can have as many tuners as there are types, so long as you only have 4 of each type (in my example you can have 12 total tuners w/o any special changes).
If you have 2 Cetons (8 tuners) installed on a single MediaCenter, you would need TunerSalad.
What TunerSalad does (not sure how) is simply removes that restriction.
I don’t know how Hauppauge & HDHomeRun do it for their 6-tuner option– I’m assuming they have whatever TunerSalad does, built into their software installer.