Which to Upgrade first? My Amplifier or Speakers?

If one appreciates phase coherency, it is next to impossible to achieve in cones. Only handful of cone speakers are anywhere close to phase coherent.

Well set up planars in a good room image incredibly well.
Well integrated subwoofers set them free.

Hi Norman,

I have sold McIntosh and Maggies since the early 80's and many of my customers have paired Mac and Maggies together and would never consider changing, if they do upgrade they stay with those same manufactures. You must remember personal taste and system synergy are critical in putting together a system, Mac and Maggies have great synergy together so that only leaves your personal taste. (not someone else's)
I am going to make a few suggestions:

1. You have a six channel amp that is rated at 120 watts into 8 ohms, having worked with Maggies for decades I would suggest you sell that amp and buy another Mac that is rated at 400 (or better) watts in 8 ohms. For around 2 grand over what you get for the MC-206 you can buy a used 2 channel MC-402 (400 watts at 8 ohm) for around 3 grand extra you can buy a pair of used MC-501 mono blocks( 500 watts at 8 ohm) I think you will pleasantly surprised at the difference in sound quality.

2. Get a used matching pair of subwoofers. Single subwoofers are great for multi channel but you must have a matched pair for quality stereo reproduction. To keep up with the speed of the maggies the subs need to be fast. You don't need to speed a lot of money to get a good sub these days, especially used. The top three subs our customers match with maggies are REL. JL audio and the Vandersteen 2WQ.

3. If you do upgrade your amps make sure you have a good electrical circuit to work with, we like to install a separate 20 amp circuit for the amps and a dedicated 15 amp for the rest of the equipment. I know in a lot of circumstances that is not possible but at least put in a good hospital grade or better outlet and we also suggest getting upgraded power cords. Again don't go crazy spending a lot of money on the outlets and power cords, there are many good products today at very reasonable prices.

4. Room treatment has been suggested and we agree. Standing waves and reflections need to be addressed but it is complicated, time consuming process and can be expensive. DSP and the like could be a much cheaper and less agrivating solution. We have many customers who have no room treatment at all and are very happy.

Gentlepersons
Thank you all for your responses.  The diversity of viewpoint, science  and opinion has been interesting, facinating and entertaining.  Some of you sent me to the dictionary; others to links with your recommendations.  Some introduced entirely different avenues to attack the issue of improved sound.  I wanted to respond to each as they came in and have individual dialogue, but I see now that you just hit Respond and address who you want to talk to for the whole crowd to read.  Regardless, I do want to thank you all for taking the time for your feedback to my question.  Very cool!  But, back to business.
The entire point of my original issue is, I love what I have and know it is good.  But, like many of you, I'm looking for the next next step up to improve the quality of aestetics - or like Robert Harley conveys, go for the purity of sound - you want to feel like you're there with the musicians (or a concept to that effect).  That is a pretty high standard and I may never get there - but damn I'm loving the journey as I know most of you do too or you wouldn't bother responding to a post from a novice like myself.  
One of you asked about the rest of my system in order to better respond to my original question.  My original post had a typo in it.  Instead of a McIntosh MP 100 (phono pre-amp) I actually have the 1100 model (8K) which is night and day better.  I've played nothing but vinyl since I got it a month ago. I also have the Kandid cartridge for my Linn Sondek turntable.  I have a subwoofer from REL Stadium II (rebuilt entirely 2 years ago).  The reason I have a multi-channel amp now is because I have a home theatre attached to it.  Maybe some day I'll have a dedicated room for sound, but not yet.  My Pre-amp is a McIntosh MX 121.  There are no treatments to my living room where the system is - though I have a 15 foot ceiling and about 20 x 30 room.  I don't own the place so I'm not investing in treatments, though I got it guys, that would make a world of difference. 
Happy Holidays to the list..
          

"I have a 15 foot ceiling and about 20 x 30 room", Norm .... I hate you already.
This IMHO is the perfect size for an audio room, especially the ceiling height. There's a cavet here though; high rooms have an inherent eco. A coffered ceiling with tile inserts would solve the isssue (hey, it's only money, ya make it every day). But as you say you're not the owner.
Also treatments tend to be NWF, so may I suggest a draping. You can hang drapes with dowels .... what ever. One guy I knew center hung a parachute with a good result. Grant it that's not everyone's cup of tea, all I'm suggesting is that there are creative, decorative, cost effective ways you can use to mitigate your accoustical issues. Fact is you have an oustanding system there, so to take it to the next level it would appear is to tackle the room nemesis.

You may also want to audition the Logan's ;-)

The horn
LOL.  Nice to know about the room size.  I've been here 16 years, but plan to move soon.  I'll look for that high ceiling.  My wife would leave me if I even suggested a parachute from the ceiling - but I got it on the echo quality.  I do have some buffer around that tampers it a bit. 
This group continues to amaze me.  Thanks for the feedback.