magnepanLRS or 1.7i ?

Your amp has enough power (300 watts/ch @ 4 ohms).  People will argue about if the amp is high quality enough, something only you can decide.  Larger Maggies allow higher sound pressure levels and have more bass.  Smaller maggies with a sub or two have a fuller range and more bass capability.  You need to establish the factors most important to you and pick which fits your needs best.  

You can literally buy 3 pairs of the LRS for the price of one pair of 1.7i.

I say go with the 1.7i and save yourself from upgrading later.
You'll get better frequency response and bigger better sound.