best integrated amp.

You can get 3.7s used for a very very good price right now.......
especially if you can go pick them up......   3.7s versus 1.7s
would provide you with a great deal more everything, but
mostly a real low end and fleshed out midrange......attributes
that no integrated upgrade for the 1.7s would provide.....

I would do both.......

get 3.7s minty used for about 3K, sell yours for 1K to 1.2K or so
then get an integrated with some punch that has been shown to gel well with Magnepan.......

All this depends on what size room you have......

May as well consider Musical Fidelity. They may not be "best" but could very well be close enough especially if value (i.e. price/quality/sound) is considered with equal weight. While most integrated manufactures liken their product to a separate amp and pre-amp, Musical Fidelity goes a step further to claim their integrated (M6si) is actually three components that happen to share the same casing. A pre-amp, and two mono-block amps. Just my .02 as I’ve auditioned the Krell Vanguard and MCIntosh comparable as well.

The new CJ CA-150 is on my list as well.

Ditto the Rogers stuff as it sounds and really looks cool, although it's pricey…I spent some time with the Kt150 version and it's sweet sounding with pure 1950s styling and only 4 power tubes which seems more civilized.

this competes with the best of them... the best for one guy,  another one, not so much,  But very nice by anybody's standard.
Coda CSIB
http://coda-continuum.com/product/index.php