Magnepan MG-1 sonically challenged?

The person who showed up and purchased my old MG-1s was very pleased. I demo'd them with a Rotel RB-1070 of 130x2 @8.
Even then, he was very happy and listened to a couple of CDs for nearly an hour.
I hope he is as happy with them as I was.
If I had them still, I'd be temped to keep them around and try them as BACKCHANNEL speakers in a 5.1 setup! I'll bet they are awesome in that context.

Thank you gentlemen, some good interesting and informative points for me a complete Magnepan novice that would like to get into to the world of planars to learn.
I am loaning the MG-1's at the moment in the comfort of my listening room. I am enjoying them very much. Love the mid range, especially drums with 'snare' drum in particular sounding really nice. What freq should my cheap as chips sub SVS PB12NSD be dialed in? The treble is a bit wishy washy though. They are musical and provide enjoyment which is what its all about eh?
Thanks again for your replies.

typically set the woofer crossover about 10hz below the bottom end of the speaker, since you probably do not have that option set it as low as you can. I imagine it would be around 60 to 80 hz.

I am a novice about subwoofers but have read there will still be output above the subs setting and below the main speaker's bottom rating - hence the 10 hz gap to minimize overlap.

My sub's frequency range is 40-120hz, I have it set at 50hz, which is a low as the MG-1's go according to a spec sheet I have seen. I am tinkering with settings, lots of time as I have just bought this pair of well kept MG's, the missus is not to enamoured with them, the oak sides are passable (just), but the beige cloth is a no-no, I think some cloth covers are going to be made very promptly. Unless I buy a bigger pair in black!

i have a pair of MG1, in excellent shape, i run them in a 3-way active crossover system, quad 303 as woofer-tweeter configuration and polk audio 10 inch active subwoofer, the sound is precise, clean and incredible,i rewire the tweeter 3 years ago with great result. it please my ears so much that never i will let go my sound kit.