nice speakers!

if you get a sub first you can set the crossover on the amp higher and the amp wont have to work as hard. this may give you better over all performance from that receiver.

BUT you will need an amp eventually as those will never sing until you get them the juice they crave. planar speakers are very telling of upstream electronics, so be prepared as the mono blocks will give you the new speaker feeling all over again. all amps are different as are their characteristics. but in general expect detail and separation unlike you have known this far, but over all the dynamics should improve by leaps and bounds and really be the biggest improvement.

all this is dependent on the electronics you decide on, so do your homework. never be in a hurry, due diligence is your friend. the migration to hifi is a personal journey, good luck and have fun.

you have many hrs of aural bliss ahead, congrats.