Second tach not possible for 912iS??

No, that doesn't make much sense.  It's a standard feature of CAN bus architecture that all devices on the network receive all data frames that are transmitted, whether they act on them or not.  The data doesn't stop at the first receiver that uses it.

Maybe there's some peculiarity to the Rotax/Dynon interaction, but even if a second tachometer won't work on the CAN bus there's no reason you couldn't install a tach that gets its signal inductively, with a small coil of wire wrapped around one of the spark plug leads.  There are dozens of them on Amazon; search for "small engine tachometer".  Check that it's adjustable for 4-cylinder engines; most have multiple settings for different engine configurations.

Thank you Eric, I will look deeper into those possibilities. I really appreciate your reply.

I would speak to Dynon directly and see if they recommend a tach (display) that can be added as Eric suggests.  Also, the Dynon engine monitor box that receives the CAN information and passes it along to the PFD is the Dynon SV-EMS-221.  I see that it has a dedicated tachometer output that is primarily intended for a signal to an electronically controlled prop.  However, this output provides one 12 volt pulse per engine revolution, so I don’t see why that would not drive a tachometer as long as the tach was set up to operate on one pulse per revolution.   Again, ask Dynon, they will know.  

Thanks Jeff, I will look into this with Dynon. BTW, your RVP set up is working great for me, thanks for all the tips!

Hi Mike,
Glad to hear your RVP testing is going well.  I just picked up a 30 gallon batch of fuel last night that I will test since we are close to the changeover time.  Hopefully I got one last batch of Summer fuel.  I believe in most states the date is September 15th, but CA has summer fuel longer and can vary by county.  Never quite sure this time of year.  Email me some info on your new aircraft!