PTHD12.7 comes with HD11 & HD10 ilok bundle licence for backward compatibiliy,
Problem#1:
Backward compatibility is something most software developers do Not understand or care..
"Upgrade=Money."
some examples:
SoundToys v5 ilok license is Not backward compatible,
Eventide same, Not BC,
Sonnox same Not,
McDSP Not,
SolidStateLogic Duende Native license is Backward v6 & v5 compatible "very rare",
WaveArts TubeSaturator2 Not,
etc...
VEP7 license, as you may guess, is Not backward compatible,
and worse VEP7 does Not have 32-Bit support, because Apple / OSX Requires deleting 32-Bit support if want to be OSX Catalina Approved.
plugin-alliance, Eventide, have deleted 32-Bit OSX support from installers, but Eventide has 32-Bit installers "if you ask",
plugin-alliance has a dedicated web page for downloading older installers, "No need to beg",
https://www.plugin-alliance.com/en/legacy/32-bit.html
same for SSL Duende Native but does Not have AAX32, v5.1.3 is RTAS only,
https://www.solidstatelogic.com/support/discontinued-products?active=7
http://eu1.download.solidstatelogic.com/Duende+Native+v5.1.3+32-bit+Installer.dmg
http://eu1.download.solidstatelogic.com/Duende+Native+v5.1.3+64-bit+Installer.dmg
http://eu1.download.solidstatelogic.com/SSL+Duende+Native+Setup+v5.1.3+32-bit.zip
http://eu1.download.solidstatelogic.com/SSL+Duende+Native+Setup+v5.1.3+64-bit.zip
etc...
VEP6 is the latest with 32-Bit support,
the latest VEP6 today: v6.0.18504
has 32-Bit support but minimum OSX is 10.10,
is Not OSX Maveriks 10.9.5 compatible.
Problem#2:
there is No 32-Bit ProTools that works with OSX 10.10.
OSX Maveriks 10.9.5 is the Latest OSX that supports PTHD10.3.10, officially PT10.3.10 only supports OSX Mountain Lion 10.8.5 but works OK in Maverks10.9.5.
ProTools HD11 supports OSX10.10 but is 64-Bit,
Makes No sense AAX32 in OSX 10.10
"Useless installer, same as latest SSL 32-Bit Native Duende installer"
https://www.solidstatelogic.com/studio/ssl-native/downloads
http://d37wi66vxsxgep.cloudfront.net/SSL%20Native%20macOS%20v6.3%20Installer.dmg
http://d37wi66vxsxgep.cloudfront.net/SSL+Native+Setup+v6.3+64-bit.exe
Maveriks10.9.5 can support PTHD12.7 also, in the same OSX, like Windows8.1x64, can install both PT12&10 at same time, in the same OS,
latest OSX that supports PTHD12.7 is Sierra 10.12.6, HighSierra 10.13.6 Audio import Fails.
The most compatible OSX for ProTools12&10 is Maveriks 10.9.5, other PT will require dual HDD with dual OSX and Reboot.
why PT10.3.10?
there are many reasons, its simpler, less cluttered menus with hundred of options most people will never use...
has support for RTAS/TDM 24-Bit plugins, also AAX32 Bit plugins.
its a bridge between old .pt and Newer .ptx
some RTAS/TDM plugins were Never upgraded for AAX. "Abandonware" like Drawmer TDM Dynamics, Rane Serato TDM Dynamics, Focusrite Forté Suite, Focusrite LiquidMix, etc...
if you upgrade to New OSX, you loose money, backward compatibility, and the ability to use what you already have.
PT12.7 has many New improvements like Fast Bounce, Dynamic plugin Processing, RamDisk cache,
but those features are only useful in jobs that require speed, like Radio or TV, for Music thats Not important.
"Depends on the Job, The Right Tool for the Job."
The Latest VEP6 that supports OSX Maveriks 10.9.5 is v6.0.16068
but is Not available in:
https://www.vsl.co.at/en/MyVSL/downloads_archive
The only available is Vienna Ensemble Pro 6 (OS X 10.8) build 6.0.15864,
and i dont know if "Check for Updates" works with that version to upgrade to v6.0.16068
Latest Firefox works OK with Maveriks,
Opera has a limit, "required an older installer" but useful features like WhatsApp still work ok.
Problem#3:
Steinberg Yamaha Vintage Open Deck for OSX does Not have VST1 or VST2, only VST3 & AU.
https://www.steinberg.net/index.php?id=downloads_yamaha_vintage_pc&L=1
V.O.D. is Not Detected by latest or older VEP6,
i contact VEP6 support, says its Steinberg problem,
i contact Steinberg support, says its VEP6 problem,
i contact Vsl.co.at support again, vsl.co.at says: "VEP6 does Not support Hosting VST3 at all, at this point."
WHAT??
basically VEP6 support does Not know why does Not work, and does Not care.
VST with 64-Bit audio was introduced in 2008 with VST2.4,
https://en.wikipedia.org/wiki/Virtual_Studio_Technology
64-Bit plugins Only work with 64-Bit Host,
and 32-Bit plugins Only work with 32-Bit host.
i have No plugins in the OSX VST2 folder, only in VST1 and VST3,
i have removed the plugins from VST3 folder, and VEP6 64-Bit detects VST1 folder as 64-Bits, that means plugins are VST2.4 ?
VEP .pdf manual pages: 3, 41 & 86, says Nothing about Not hosting VST3.
VEP6 has a VST3 plugin for DAWs that support VST3, but VEP6 does Not host VST3, Crazy...
plugin-alliance VST plugins work in 32 & 64-Bit VEP6 Host, but has No VST2.
VEP6 does Not support a plugin format invented 11 years ago. Crazy....
other VEP6 alternatives?
ddmf.eu Metaplugin & Bridgewize 32-->64 only, Not Catalina support.
nugenaudio.com sigmod
BlueCatAudio PatchWork
Fxpansion VST to RTAS adapter v2.x, "Only works with VST1" "Abandonware"
NI Maschine
Reaper ReWire $60usd. version.
VSTLord
Problem#4:
Motu Volta latest installer is Not Maveriks compatible. "Abandonware but still for sale."
Problem#5:
Roland SH-201 Editor Librarian is Not 100% Maveriks compatible.
Problem#6:
Latest OSX Sierra Bootloader / Bootcamp requires a New Windows 8.1 or W10 Clean install.
Older Maverikx Bootloader does Not require a New Windows clean install.
for Video Editing, there is basically No other option, Digital or Nothing, Analog alternative is to tedious.
but for audio things are not as black & white, Analog still is 100% compatible, and a good alternative for most cases "best option".
if you do Not want to fall in the Upgrade or Die, install configuration bug compatibility nightmare, the only option is OutTheBox.
The only Analog incompatibility is the impedance-Z and the levels, Nothing more.