Just an update on my experience :
After support team contacted me, I made a try on Spark2.
First, I was wrong to consider it as a different product. It actually replaces spark 1 (plugin name remains "Spark").
The good news is Spark 2 is compatible with both PT10 and PT11 :
=> it correctly open previous insances made with AAX version (meaning made with PT11 as Spark 1.7.x wasn't PT10 compatible).
BUT :
=> it still not open directly session created with Spark RTAS (.dpm)
Apart from all of this, I changed my mind and I am really enthusiast with Spark2 update :
I like the new GUI and new features, even if I discovered few bugs.
The new GUI is more "epured" (no more animation) and the old VDM/EDM GUI is still there and compatible with the 1st Spark Controller.
So I hope it would also help having better stability and performances.
But, first, I need to "convert" all my library. I don't have that many, but I must open all my old session to be sure. And to do this, I had to get back to v1.7.2.
So, personally, and for people who have tons of Spark RTAS sessions, I don't recommend to update to Spark2 straight away (v1.7.2 and v2 can coexist but are sharing many files => so v1.7.2 often crashes, especially when attempting to open library browser).
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BEFORE updating to Spark2 :
1/ make a backup copy of your library (for safety)
(NB : by defaut located in [System HD]/Library/Arturia/Spark/Spark Library/)
2/ (option) I advice to open each PT session that uses Spark RTAS with PT10 ; and add your spark project name in each instrument track's comment (to remind later when you will load Spark2 AAX)
3/ (really important) export each of your spark project, 1 by 1, as ".spk" (it is a unique embedded file containing all needed files). Later, you will import them into Spark2.
follow this link (even for Spark CDM)
NB : You can do that with PT10, or with Spark Standalone
4/ (option) Make a copy of Spark.dpm somewhere*
( Just in case you'll need it to re-open an older RTAS session later)
NB : loading dpm version won't work well but could help in some situations
5/ Then you're ready to update to Spark2 (clean update recommended)
(* typically : " /Library/Application Support/Digidesign/Plug-Ins (Unused) " )
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I hope it would help PT users...