I think an integrated Danfos valve is a different situation than a separate AS system that is only included in the field.
I consider ball valves riskier than the 6/2 itself. The outer lever can always be pushed by something. You would have to properly protect against accidental shifting because instead of security, the cause of an accident may become. Ideally, you would use a lever lock valve that reqires pusch, as sometimes used on the front linkage.
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I think that, however, I am wrong, since the balls are to be an additional cut-off, closing them or opening them will not block the steering wheel.
If you continuously check the correct position of the hand lever with safety related parts (1oo2) and you warn (prevent from driving on the road) the driver it will be the first major step.
The ball levers are just a SECOND security though, the 6/2 valve is always off to block flow on the road… as well as power totally cut to the proportional valve. Do I actually use the lever valves? Ill leave that up to you to decide…the point is there is 3 systems in place, and it is literally impossible for the tractor to steer on the road, a stock hose / component is far more likely to fail and cause harm.
BUT sadly as impossible as it can be, it really makes no odds, at the end of the day its a modified system, with no certification, and I am fairly confident in the event of an incident, it would be a real headache. I just hope that provided the accident wouldn’t ACTUALLY be caused by a steering failure, and the fact it has multiple safety systems, that it would be possible to avoid major problems…
Its something Id love to know more about, as I would much prefer the peace of mind knowing it was legal / not likely to be an issue for me. I have 100% confidence in the safety of my system, I even have a switch on the gearlever that alarms a loud buzzer if you use the top two ranges of the transmission with the autosteer lockout not engaged, but its still something on your mind that the insurance company could use against you, even if the accident was totally un-related, which it always would be!
Does anyone know how 3rd party companies go about making there hydro steering systems legal?
For me its worth the risk as I am owner operator on any of my equipment that has a steering valve, and I really dont want to have to use a steering motor, the hydro is so clean and smooth.
Not sure there will ever be an answer though…
I will try to find out what needs to be done for legalization.
Daren had a factory steering system failure on my MF5455. The tractor was practically new, it was less than a year old, the connector at the piston broke, it was soldered in 2 pieces and it gave off solder. I had a lot of fear because I was driving on a busy road with a trailer and I lost the steering, I miraculously missed the truck … I also want to laugh at these certified, supposedly safe factory systems.
I completely agree, I am 100% confident my system couldnt cause a steering failure, more so infact than a factory steering valve of which could be open to any form of failure that I do not know about. At least I know my system is double isolated and safe.
Sadly its not just about that though and without the right paperwork, its just as bad as anyone elses setup 
At work I drive a company mounted SBG sytem. Only security I find is the warning on the screen at startup that says “you must not drive on the road with activated system” , and WHEN system is fully activated, there is a the click of a relay when I press autosteer on the screen.
If by accident the 6/2 blocking valve (inbuilt in steering block) should be energized (get 12 V ) then I would not be able to steer at all.
On a CNH T6 with factory built autosteer, there are a relay for each pwm coil. When Autosteer switch is on they are activated and connects one wire of coil to PWM feed while the other wire is to GND
And the “dump valve” (6/2 valve) is fed from UCM controller via wire 3168 and the other 3169 is to GND. But I don´t know which CAN conditions will tell UCM to feed wire 3168, but I KNOW that if I feed wire 3168 with 12 V, then steering by steering wheel is impossible/blocked!
So I would say your system darrenjlobb would be even more safe 
The “weak” point in both systems are the 6/2 valves!
I agree, as when on the road my valve block is isolated by the 6/2 valve, and the solenoids are isolated by relays (which if still get power, beeps buzzer if in top gear), and also have the manual shutoff valves if you want extra saftey…SO really better than OEM, however in an accident, the OEM system wouldnt even be looked at, but mine would likely prevent an insurance payout!