I do believe the 8.1 Piranesi Out was not great. It was improved in 9.0.
If you have Artlantis, It produces a good Piranesi File.
You might try making your 8.1 rendering size smaller and or less complex.
You might also try saving your ArchiCAD Rendering as an image say a TIF and using Piranesi / File/New Create an EPix file from an Image file.
An Epix file is a TIF with additional information. So you will not have the additional information ie: Material and Depth, but it might serve you in a pinch.
David Pacifico, RA
AC27 iMac i9, 32 gig Ram, 8 gig video Ram