This is an active crossover plate amplifier that has filters tuned specifically for the drivers and enclosure it was attached to. Connecting it to a different set of drivers in a different enclosure through an existing passive crossover is not going to produce anywhere near a flat frequency response. TruePlay is just a simple room correction software that utilizes the microphone in an iOS device. It is not going to modify the crossover settings to match the new speaker and I doubt it will be able to overcome the terrible frequency response created by doing this hack.
I was thinking the same. A heavily DSP’d box that is tuned to sort out some of the worst vibrations and modes certainly isn’t going to perform well with the generic bookshelf loudspeaker.