If I offened I apologize. I wasn't aware we were discussing Brazing. Nor was I aware the question was for advice on purchasing equipment. I just took the question straight on.
To the best of my knowledge preheat and PWHT dose not even approch the upper transformation points of most metals.
We skirt a fine line with the Tempering temp sometimes though.
In my line of work HAZ is a very big issue as is dillution.
What problems did I say could not be managed?
What did I say against Oxy/fuel Brazing? Oxy fuel welding is slower than GTAW and requires much more BTUs than GTAW and sir if you are dealing with a very expensive finished machined items this are not small matters.
I also have a good deal of time with Oxy/Acet High temp Silver Brazing on Turbine blades plus PTAW for the same purpose.
When you say heat management followed by the metals are same no mater how you heat them confuses me. Heat is the engine of change for metals. normalizing, anealing,Harding and tempering are acomplished with heat and oh yes stress relieving.
Again I apologize for nor reading between the lines.
By the way, I recall Aluminum being mentioned. I have done my share of Oxy/Fuel welding of Aluminum as well as GMAW and GTAW. Enough to know I sure don't prefer Oxy/Fuel over the others for any reason.
If you attempt to weld (Oxy/Fuel) on a large section of Aluminum you will learn alot about BTUs.