If you are willing to spend $60-$80 on another pair of full range drivers, why not spend the same amount on a pair of tweeters to play with to compare full range to a tweeter? Even if you only have 4 channels to play with, replace the midbass with the tweeter for a while, readjust the crossover slopes and give it a listen? Or even go with a tweeter on a simple cap to highpass and coil to lowpass the midrange and run the, active? Or even a predesigned textbook xover from PE just to experiment with a 3-way instead of full range? Making a system that sounds listenable isn't that challenging. Get the TA set and kill a couple of the annoying peaks and most people will be happy. Especially when you have nothing to actually compare it to or don't have much experience with an actual high quality reproduction. That's where I think the fallacy is here.