Let's try this a different way then

It appears my desired Maggies will not work in my 13x22x10 room, so I am now in search of the next best thing.

Which speakers (especially those listed on the marketplace here) under $1000 would be well matched to my Adcom GTP-500/GFA 555? Source is an Onix XCD-88 (Burr-Brown 1732 24-bit/96kHz DAC internal).

Musical tastes are folk, jazz, classical and 60s rock. As you can tell by the reference to the Maggies, soundstage and detail are more important than bass. Ideally, I'd like to fill the room with music and lose track of the speaker locations

I have a pair of Martin Logan SL3 speaker for sale on the Audio Asylum Trader. Excellent speakers for anywhere near their price. My room is very similar in size to yours but my ceilings are only a little bit over 8'.

There is a link to the Sterophile review in the ad

There's no reason smaller Maggies wouldn't work in your room, probably best along the long wall. 1.6s might be a good choice if that's your cup of tea.

IMHO, small point source monitors are best at disappairing and throwing a big soundstage. Consider Reference 3A, Proac, Totem, Focal

You can always add a sub later. Cheers,
The new Magnepan MG.7s are stunning and would work well in that room. New they are only a little bit more than your budget.
First off, after owning MG12s and MG1.6s I can say I'm not a Maggie guy. While I can hear the virtues in them, they just don't convey the music to me in a way that lets me relax and feel it. Always find myself listening to the speakers/system in a technical way.
My last try was with the 1.6s and it didn't take long to realize they weren't my thang. I gave them to my grandson. While we were dismantling the Maggies, I had my Revel M20s playing the music I had just used to demo the 1.6s for the boys. Everyone agreed the Revels sounded better. Even my 84-year-old dad thought the Revels had more going on.
Under $1000 you need to look at used. I agree with Sbank above, except I'd through Revel and a few others in the mix.
There is a pair of Spendor S3/5 monitors listed here for $650. Put
those on a nice set of stands and I think you will like them. You
would even have some cash left over for a sub if you think you
need it! BTW, $650 is on the high side for those speakers.
I think the Adcom would sound a little ragged driving the Magnepans
I love Maggie's, that being said, that is a long narrow room, indeed. Small monitors with a sub is a good recommendation. There are too many choices.....so get your self out to your local dealers and listen.
Maggies are quite forgiving of proximity to sidewalls because they have nulls off to the sides, being dipoles. They also like a lot of breathing room behind them, again because they're dipoles. So unless placement constraints prevent you from taking advantage of your room's long dimension, you might not want to cross them off your list just yet.

There's a pair of Joseph Audio RM25s for sale here for $800. Outstanding imaging/soundstage and they pull off a disappearing act that rivals the best out there. Will have no problem filling your room with sound. Jump on them. You won't be disappointed.
No planar speakers are going to, "fill your room with sound." Whether electrostatic or planar-magnetics; they are way too beamy. Done correctly; they do an excellent job of disappearing, as a sound source, but one must be seated in exactly the right spot to enjoy the presentation. You won't accomplish what you want(filling the room) with dipoles. An omni style system would be a better choice(ie: in your price range- Ohm).
I agree with Soix get the Joseph audio RM25s
Other than a higher ceiling, my listening room dimensions are quite similar to yours. I've used MMGs (with subs) across the long wall with superb results. As Ralph notes, they'd probably be fine on the short wall, too (given the response null to the side), but my room isn't laid out that way. Without the subs, bottom end response is too limited for my taste, but the room size is almost ideal for the speakers, IMO.

Sorry, that should have read "as Duke notes"
Agree with Duke. If you like the Maggie bipolar planar sound, having distance to both front and rear walls is the key for optimal results. Distance to side walls matters much less. The best Maggie setups I have heard have the speakers 1/3 the depth of the room or even more out from the front wall. That's how teh famous Jim Smith used to set them up years ago at Audition in Birmingham Alabama, where I first heard and fell in love with them. Unfortunately, its not a configuration that is marketable or practically works well for many, so you don't see it as often as one would expect.
Tannoys also image like crazy!!