Hey douglas. None of these op amps will cause damage if they are put into an un-modified device. Don't even worry about that. They are all designed to work exactly as a standard monolithic op amp. However, these high current discrete op amps can sound somewhat bright/thin and have a solid state harshness if they are starved for power. Looking at internal pictures of the Minimax, I can see that there are some capacitors close to the op amps, but I cannot tell if these are power supply caps or if they are DC signal blocking caps. In any event, if you want to try out different op amps, go for it. As I said, the Sonic Imagery are the best in my opinion, but they are absolutely huge and will not physically fit in some locations. The Burson V6 Vivid is second place and gives a little less resolution and more warmth, but it still has more overall resolution than the Sparkos. The Sonic Imagery are the most demanding, but even the Burson V6 Vivid and the Sparkos can sound a little thin/bright without good power. Making sure you have a good amount of power capacitance very close to the op amp will make the op amp sound smoother and fuller.
I have tried the previous generation NawClassD op amps and regulators and was completely unimpressed with their stuff. The op amps were the Special Edition with super fast slew rates. In some ways they sounded better than monolithic, but after some time listening, I could tell that there were problems with the sound and resolution/air. The regulators were complete crap and made any equipment sound like low resolution consumer electronics. I have not tried the new models they have release. The design is different and uses different discrete components, but I don't know what the result is.
The Sparkos regulators are absolutely amazing! I recommend them for replacing any existing 78xx/79xx voltage regulators (if you are adept at desoldering/soldering projects).
In my opinion, the best monolothic op amps are opa627, opa827 and ad797, but all three of these have compromises in one fashion or another and are not as good as the discrete op amps.