I just got an answer to an email to Lasersoft...
Dear Mr. Arbib,
Q1 ({a}can I install both versions on the same computer?, {b}Can I run both at the same time?)
Answer - {a}
You can install both versions on the same computer, as long as you are not running Mac 10.7, 10.8 or Windows 8. These three operating systems are not supported with the SilverFast 6 software. Since your scanner is a new purchase (as long as not a second hand purchase), the upgrade to the SE 8 will be a free upgrade for you. You can only request this upgrade within three months of your scanner purchase, otherwise the offer is void after three months.
(Answer - {b})
You can have both software's installed, but you can't run both versions at the same time. If you have one version open, the other version will not launch. So to answer the "run both scanners at the same time" question, the answer is no. It is not possible.
Q2 (If Q1b is No, do I need to unplug the scanner I am not using?)
You don't need to unplug the scanner not being used, but you do need to make sure it's turned off.
Should you opt to request the free upgrade to the SE 8 for your Epson scanner, it is still possible to have both scanners connected to the same computer and have both installations on the same computer. The installations are separate. The Plustek installation is different from the Epson installation. When you launch SilverFast 8, the scanner is listed in the Image Source. When you have SilverFast 8 for both scanners, you make sure the scanner not being used is turned off and the correct scanner should be listed in the Image Source. There will be no conflicts with having SilverFast 8 for both scanners, even if one is SE and the other is SE Plus.
Best Regards,
LaserSoft Imaging, Inc.
625 Freeling Drive
Sarasota, FL 34242
Office: (941) 312-0690
Fax: (941) 312-0608