The answer to running Jam 6 on an Intel Mac Pro (Nehalem 2009-2012) is YES it does work.
Now for the details.
You MUST have Snow Leopard (any version) installed with Rosetta.
Create a Folder named "Roxio Jam 6" in your Applications folder.
I have Jam 6 on factory CD installer. (also have valid serial / activation numbers)
I could NOT get Jam 6 to run despite no errors or troubles installing.
Jam 6 would try to launch but nothing would happen.
I am not a software geek but I do have a good idea why it would not work.
Previous versions of Jam required a disc burner that was SCSI or ATA/IDE/ATAPI. (optionally firewire)
Intel Macs have SATA interfaced disc burners.
Eventually I stumbled on to a solution that is very simple.
Download Jam 6.0.3 updater.
Install Jam 6 using that updater. (drag into the Roxio Jam 6 folder you created)
Do not use Jam 6.0.0. or 6.0.1.
When I tried this, everything works as expected.
I have not tried "ALL" features and processes but I did use Jam 6.0.3 to burn a CD without error or flaw.
No surprise.... Jam 6 reports "unknown interface" with all my installed disc burners. (I have both DVD and Blu Ray optical drives)
Regardless of this error everything worked.
I was even able to use files from OS9 Adaptec Jam 4.
I am not certain if this makes any difference but it should be noted.
I have either Toast 9 Titanium or Toast 10 Titanium installed PRIOR to Jam 6 installation.
It IS possible that the Toast drivers allow or enable Jam 6 to function properly with SATA optical drives.
These drivers "may" be required for Jam 6.0.3 to function properly. (I don't know for certain)
What I can attest to is that Jam 6 does function on a Nehalem Mac Pro running any version of Snow Leopard with Rosetta installed.
I am running OSX 10.6.8 on Nehalem Mac Pro 2009, 2010, 2012.
(actually I am running 10.5, 10.6, 10.7, 10.8, 10.9, 10.10, and 10.11 all on separate hard drives or separate partitions on Nehalem Mac Pros, this is achieved through use of compatible video cards otherwise you are restricted to 10.8 and above, best options for multiple OSX compatibility from 10.5+ ARE.... NVidia Quadro FX 4800, NVidia GT 120, Radeon 4870,.... best for 10.6+ IS Radeon 5870, NVidia Quadro FX 4800, and Quadro 4000 as well as all others mentioned.... among them all.... the NVidia Quadro FX 4800 is the ultimate Swiss Army Knife video card with only one downside, its output is DVI ONLY, cannot be used with an Apple DisplayPort monitor.... note that OSX 10.5 on Nehalem Mac Pro requires an Apple (non retail) installer disc AND either the Radeon 4870 or Nvidia GT 120 video card or it cannot be installed, once updated to 10.5.8 you can upgrade the video card to NVidia Quadro FX 4800,.... Radeon 5770, 5870 and Quadro 4000 are incompatible with 10.5.... NVidia Quadro K5000, the best of the best "workstation" video cards, requires 10.8 or above)
You CANNOT install Snow Leopard on a Nehalem Mac Pro with a retail Snow Leopard (10.6.3) installation disc.
It is impossible even if you transfer Snow Leopard from a non Nehalem Mac Pro it will Not function "fully" or entirely properly.
The reason is due to Hyper Threading / Turbo Boost only available on Nehalem Mac Pro hardware.
Snow Leopard 10.6.3 retail installer does Not contain the correct system code and thus, cannot be used to install.
The installation of Snow Leopard on a Nehalem Mac Pro requires an Apple Factory (non retail) disc that is OSX 10.6.4 only available directly from Apple.
This non retail factory disc has the proper Nehalem version of Rosetta on it but it does Not automatically install.
Installation of Rosetta is an Optional Install.
(all Snow Leopard Rosetta installs are Optional Installs, none are automatic)