I need to downgrade from 10.11.6 to 10.11.3

[jamesleonard]

Hello I need to downgrade from 10.11.6 to 10.11.3 (El Capitan)

Because I have:

• PT 12.5
• 003 workstation (Control Surface)

System Details
• Computer: 27-inch iMac (i7)_5K Retina display: (El Capitan OSX 10.11)
• Processor: 4.0GHz quad-core Intel Core i7, Turbo Boost up to 4.2GHz
• Memory: 32GB 1867MHz DDR3 SDRAM - four 8GB
• Storage: 1TB Flash Storage
• Graphics: AMD Radeon R9 M395X with 4GB video memory

First of all I'm sorry if I am asking a dumb question!

However, I have been told that:

• I need a back-up made from: 'Time Machine' or;
• If not, I will have to see a '3rd Party'

I know:

•Support for OS X 10.11 (El Capitan) was added with Pro Tools 12.3. OS X 10.11.0 - 10.11.3 supported
•Mac OS X 10.11.4, 10.11.5 & 10.11.6 are not qualified and not recommended for use with Pro Tools

Also know OS X Sierra is not qualified yet as well (not sure if Sierra will ever be compatible with my 003)

So... Just to reiterate - what action do I take now?

Many thanks to all in advance!

James

P.S. What Lead/Cable would I need? (i.e. from: '003 Workstation' > 'iMac')

EDIT//: It seems that - I will need the 'Apple Thunderbolt Male to FireWire Female Adapter.'
Once I obtain this adapter, I will keep using the original 'FireWire 800' cable (which is connected to the 003) and connect the: 'Apple Thunderbolt Male to FireWire Female Adapter' to the 'FireWire 800' cable and then connect this to the iMac (Thunderbolt 2 port).

(see link below):

http://www.maplin.co.uk/p/apple-thun...-adapter-a08lt

EDIT//: After a consultation with apple UK (about downgrading to 10.11.3) - they gave me the telephone number of an independent, 'apple accredited' business - who 'can downgrade' for: £27.00. I like the way apple delegates work to other independent businesses - especially, if apple don't/won't - want to do it theirselves