How do the Magnepan 3.6r compare to the new 1.7

3.6, it's not even close. Deeper, wider, and much louder.

Read a review on Audiocircle comparing the two but can't immediately find it. Reviewer said the 3.6 was much better than the 1.7's. I have 1.6's and 3.6's and the 3.6's rule. Higher resolution because of the true ribbon tweeter, deeper bass and much more dynamic

You can get a great killer deal on a used pair of 3.3 or 3.5 that the new 1.7 can't match either. The 3 series is altogether in a different performance class. The core implementation of each series will never allow a 1 series to perform like the 3 series.

First consider your room size, a small room with 3.6's can underperform 1.7's in an optimal room. Also 1.7's are more seamless and coherent across the 3 way whereas the 3.6's might have some discontinuity between the ribbon and bass panel, some can and others cannot discern it.