I would look at a different amplifier with more current delivery. All Magnepans thrive on power, the more the better. Within your budget there's plenty of options, especially if previously used is acceptable.
I don't have personal experience with the 1.7i, but I've used various Maggies for over 20 years (currently the 20.7) and they all need a lot of juice to come alive. All your concerns will be resolved by using more high quality power. Even the bottom end will seem to go deeper. Adding subs to Maggies will do that too, but not necessarily to your linking. And it won't address the other concerns.
I don't have personal experience with the 1.7i, but I've used various Maggies for over 20 years (currently the 20.7) and they all need a lot of juice to come alive. All your concerns will be resolved by using more high quality power. Even the bottom end will seem to go deeper. Adding subs to Maggies will do that too, but not necessarily to your linking. And it won't address the other concerns.