If you do go with amazonia there are two options I see.
(best choice)You can do a live swap, doing it in sections and over periods of time (like 1/4th one week, another 4th next week) but you will have to keep testing your parameters to make sure it doesn't get too bad. I personally did this and had great success, the ammonia barely showed up and my oto's seemed to be healthy over the 3 sections I did (mine is only a 6 gallon tank, so ALOT riskier than a 40b)
** WARNING: i wouldn't do this method if you have real sensitive shrimp or fish **
(ok choice)You can setup another container with the substrate and let it leech out but it will typically take a month or so with some sort of filtration and W/C's. This doesn't void it from still causing a spike of ammonia in your main tank but it will lessen the blow. I have done this as well in my 6 gallon and I didn't see any ammonia spikes from the rescape.
(sensitive fauna choice) doing both together - let it leech in a container for a month or so, and adding it in sections to your tank. Definitely a PITA scooping old substrate and adding new in.
I can't say anything about eco because i've never used it. I'm no advocate of ADA - It's just if it aint broken, dont fix it kind-of motto.