I recommended the subs because I have successfully done it. The DOGMA against integrating subs with Maggies is that the Maggies' rise time (i.e., speed) is too far ahead of subs you'd put with it. That may have been true ten years ago, but there are many fast self-powered subs today.
I have two very small (9" cube) Mirage MM8 subwoofers in stereo. They aren't the deepest, but I've had little trouble integrating them with the panels and adding nearly an octave of bass extension and in-room power response.
They really popped into focus when I used a mono source and tuned the subs' phase controls (a continuous 0-to-360 deg. knob), one subwoofer at a time, until the bass snapped into focus.
The other approach as Lostbears mentioned is the Magnepan bass panels. They are so fast their frequency response can extend up to 7 Khz, so there's no problem matching speed and rise time in the 40-80Hz region. If you have the room and placement options, they're a perfect augmentation to the 1.7s. You get a piece (or two) of the 20.7 bass panel but a lot more placement options and a lot less cost than upgrading to 3.7i's.
Finally, I agree with Zd542 that the 1.7's bass quality is excellent. However, unless there's a fluke in the room acoustics or a miracle in speaker placement, you may--as I did--ultimately find the overall tonal balance a bit thin and wish for more bass quantity. One or two DWM panels or small sealed subs (such as JL Audio's Dominion d108) will do the trick.
You still won't get subterranean bass, but you'll get good sub integration and a very engaging tonal balance. You'll no longer have to listen around the 1.7's quick rolloff that starts around 55 Hz.
