Can you create a 16 channel PRIR from two 8 channel PRIRs recorded on the A8?
Theoretically yes. Two 8 channel PRIRS could be converted to the A16 and with the A16 a listening room can be populated with speakers from different PRIRs.
BUT: The A16 works with speaker designators: If you want to create a listening room and add a left top front speaker for example, then the designator is Ltf and it has to be recorded in the PRIR as Ltf. With the A16 no problem: You can even create 16 PRIRs, for each speaker one, but with the A8 I don't know at the moment if the A8 offers all the speaker designators that the A16 needs for a 9.1.6 room for example. If so, then maybe this could work. This would mean you have your normal 7.1 speaker PRIR with L,C,R,SW,Lss,Rss,Lb,Rb and then you would have to place your speakers to the missing positions like the wides (Lw, Rw) and the tops (Ltf, Rtf, Ltm, Rtm, and so on) and record a 8ch PRIR with these speaker positions and the correct speaker designators, IF the A8 does offer those.
So you would have a second PRIR with Lw,Rw,Ltf,Rtf, etc. and both PRIRs would then be ported to the A16 and you could populate a 9.1.6 room with all the speakers from those two PRIRs. But I think the A8 does not offer all the necessary speaker designators. And even if so I don't know if this would really work.
-> Manual p.27:
https://smyth-research.com/wp-content/uploads/2019/06/A8manual_08_2011.pdf
So, wouldn't work because there are not the necessary speaker designators.
I think however, that the Smyth could change the speaker designators, but this would be a special individual service.
If so, could I take one of the existing PRIRs and move the virtual speakers around (including upwards) to create an extra 8 channels? Will the virtual surround be as good as with a 16 channel recorded PRIR?
I don't understand the question. What existing PRIR?
A "virtual speaker" can not be moved spatially afterwards. If I understand this correctly, you think you can record for example a left front speaker at ear height and then do some "magic" inside the realiser and this gets a left top front, or right top mid or etc...?
No this doesn't work. A speaker HAS to be recorded in the correct position relative to your ears. So if a left top front speaker will be recorded it has to be at the left top front physical position if you sit upright and look forward.
Note that I said relative position!
You could then turn around 180 degrees so that this speaker would then be a right top rear speaker.
For example a couple of guys and I recorded each one 8 PRIRs, using just two stereo speakers at ear height and two top speakers. By rotating the listener relative to these speakers we recorded 12 positions at ear height (L,C,R,Lw,Rw,Ls,Rs,Lss,Rss,Lb,Rb+SW) and 4 top spakers (Ltf,Rtf,Ltr,Rtr).
If (1) doesn't work then does anyone know if Surrey Uni would allow me to record a PRIR?
Well, I think the Surrey Uni would know best...
Why not ask them?
I think this could be the right link:
https://www.surrey.ac.uk/centre-vision-speech-signal-processing