Hey guys, I'll take a stab at this one since nobody else has answered our new "first poster" and that's too bad.

Jeff it has been my experience that a high ceiling increases the volume of the room thus you may need more powerful speakers and amplification to make up for the increase in space.  As far as room shapes go, however, there is nothing inherently bad about a vaulted ceiling.  It may even be desireable.

The reason I say that is because the good news is that a cathedral ceiling generally LESSENS standing waves so the room may have increased potential for lack of muddiness.  A lack of mud is a GOOD thing.  

That being said, what you may have to address is the lack of furniture and walls that would have kept the overall long wave reflections down to a dull roar if it were a more normal room  I.E. a room with an open ceiling is often  a "sparse" room as far as items that help break up slap.  Not so much because of the ceiling per se but because from an interior decorating standpoint an open floor plan inclines most folks to leave the whole place pretty bare.  And a bare room can cause slap echo or even some long wave reverberation like in a real church Cathedral.

I had a friend with a huge room and he used Maggie Tympani IVs which are humongous flat panel ribbon speakers six feet tall and four panels total each panel about three feet wide as I recall.  He pushed them with two banks of extremely powerful tube amplification using custom designed electronics.  The biggest problem I had in designing his space was to get his listening position out into the middle of the room away from the walls and in the correct tip of an equalateral triangle so that he could get a perfect "stereo" image.  I wound up putting the listening sofa and club chairs in a circle facing inward so that you had everybody arranged for a conversation pit and the sofa was a perfect listening chair facing his Maggies.

The speakers in his case were a classic "line source" with practically zero first reflections (Maggies are like electrostatics in that respect).  And the size of the room was a great help in making for a pure, uncluttered soundfield.  The big problem as I recall was that his wife initially had all the chairs scattered around the room with large potted palm trees placed directly in front of the speakers to "hide" them, haha.

Building a conversation nook won her over as my design actually looked pretty hot and boy did the speakers sound better once the plants were removed from them! The sound arriving at his sofa was pure and sweet and huge, like only the big Maggies and a few other designs can do.  I do wish he would have followed my advice and built some support braces to experiment with tilting his Maggies back to lower where they threw the image.  The image was just a tad too high for believablilty as a stage, but all in all the sound was astonishing in general so I was pretty gratified.

If you use box speakers in such a room I would suggest building some huge thin decorative panels that look like a Jackson Pollock painting perhaps 8footX4footX6 inches with something attractive silkscreened on both their "canvass" sides and the insides of the "paintings" stuffed with loose fiberglas bagging.  Hang four or six of these discretely around the room about three feet off the walls wherever it looks and sounds best. These would give the bottom end some tightness and kill long wave reverb if it is a problem.  

Box speakers, unlike electrostats or Maggies would tend to need these panels the most as box speakers send out reflections all over the place and while this makes for a wonderfull sound throughout the room it also creates more problems that require damping.  I have a bungalow that has a Southwest look in several rooms-so hello Indian Blankets on the walls!  And in another space I went all Medieval and hung a huge Flemish tapestry on the wall behind the listening sofa.  These absorbent materials helped make the rooms cohearent and got rid of the blurred soundfield that had initially emerged.

You might instead build two dozen two foot tall by eight foot long versions of the same fiberglas filled panels and make several dozen of these and hang them above the listening area real close to the ceiling to do much the same job in a huge cathedral shaped room. The basic idea is to provide some general room dampening against echo because you don't have enough furniture and diffusion because the room is so bare.  Thin panels hung discretely usually just looks like some sort of attempt at "art" and doesn't disturb the sensibilities of our interior decorator friends.  Meanwhile the panels do a super job as tune-up tweaks for us Hi-Fi nuts without getting us caught in a fight over room designs.

I would recommend you purchase Jim Smith's book "Get Better Sound" and perhaps the Yamaha guide to concert public address music systems to see what a professional system of room tuning and attention to acoustics could do for you.  I have no financial interest in pushing Jim's work however he has amassed pretty much what I learned the hard way over a forty year career building playback rooms.  You buy his book, you become armed with the correct information and will soon be on your way building great sounding spaces.  It just takes some book learning if you would not mind doing your homework like a good boy...  I am still buying books on acoustics and learning new tricks even at my advanced age.  I envy anyone getting all this stuff early on as great sound happens only to those that work the room.

In any event you are to be greatly admired for posting a first post about the most important part of our hobby, acoustics---and asking the best first question I have ever heard.  Instead of "how do I spend more money" you asked "how do I fix the bloody ROOM?"  

You are on the path to becoming a true audio creator and will, I predict, one day own a completely intoxicating music room where you can use your set as a time machine and hear recordings come alive for your intense pleasure and education.

Good going!