For the purpose of testing, I would suggest manually setting the crossover for all three front speakers (including the 590's) at either 100Hz or 120Hz for the purpose of comparing them to see how they will work together.
Obviously they will sound weak, but once you have subs I would expect you will likely cross the 590s at 60, 80 or 100Hz and the 520 at 100Hz or 120Hz.
The 590's have much larger woofers (remember, it is the total surface area times the stroke distance, not diameter that really matters!) and the 520 is a sealed cabinet, while the 590's larger woofers are ported. Definitely expect them to sound different if driven full range!
From the standpoint of timbre matching, our ears are much more sensitive at the midrange frequencies. That is the reason you don't get much concern over which subs you match with your speakers. You want to get good subs, but among good subs, one is about as good as the next, it becomes more about looks and features!
