Alrighty!
If acoustic treatments are out of the question, then that is a pretty serious consideration for your choice of speakers. There are kind of two ways that you can look to address your room's acoustics with your choice of speakers alone: you can go for speakers with very narrow dispersion that sort of "beam" the sound to where they are pointed and thus, interact as little as possible with the room itself, or you can go for speakers with extremely even off-axis response so that the reflected sound will at least be predictable and that wonderful computer in your head that we call a brain will have a somewhat easier time "filtering" the audio that it receives.
This is a very large room - well over 10,000 cubic feet and as much as 12,000 cubic feet if the ceiling is 20 feet high rather than the 18 feet high that you mentioned first. Regardless of the ceiling height, the size of the room is going to demand some very, very capable subwoofers and it would not hurt at all to also use efficient speakers that are capable of high output levels.
You have a nice selection of some very good speaker brands available to you through your dealer. But you also have options in that list that have rather distinct "characters" to the sound. Klipsch, for example, might be a very good choice since their speakers are extremely efficient, capable of very loud output and tend to "beam" a bit. But there is definitely a "character" to Klipsch speakers. Your father might really like that particular character, or he might hate it! An audition would certainly be necessary.
I'm quite a fan of Paradigm's Signature line of speakers, but their largest towers and center speaker would eat up the budget rather quickly! I'm not as much of a fan of their "Reference Studio" line, which I personally find to be overpriced for the performance.
Martin Logan, with their electrostatic speakers, could be a good option as they tend to have a narrow "sweet spot" and limited dispersion. But they aren't the most dynamic speakers and being a true di-pole, they will still interact a lot with the room's acoustics.
It's a tough decision! Speakers can be such a personal preference and in a large, acoustically untreated room, it's really going to depend mostly on what your father likes.
If you are willing to consider an internet direct brand, a good option would be Aperion Audio's Verus line of speakers. They can play very loud with almost no distortion and they measure very nicely in real rooms, not just anechoic chambers
As I mentioned, you're going to want a tremendously capable subwoofer setup. From my own auditions, I was extremely impressed with the newest SVSound PB13-Ultra DSP subwoofer and a pair of those would have the output capabilities and audio quality to work well in that room. Certainly, the brands that your dealer carries also offer very good subwoofer options, but you won't find the same level of output and quality for the same low price as what SVSound offers with the PB13-Ultra DSP. As others have suggested, Rythmik also offers some very good subwoofers, but the SVSound Ultra is even a cut above those, IMO. The slightly smaller, slightly less expensive "Plus" models from SVSound are pretty much neck-and-neck with Rythmik's best offerings.
If you can control the lighting in the room and a front projector is "out of the question", then the most obvious choice is a 65" plasma from Panasonic. If the distance from seats to TV screen is closer to 10', then the 65" size would work quite nicely. If the distance is closer to 15' though, that 65" size is going to be too small. At 15' from the screen, the
smallest size you would want would be 80" and 110" would actually be the SMPTE recommended size at 15' !
So if the seating distance is further than 10", I'd recommend giving serious consideration to a Mitsubishi rear projection DLP. Without question, the Panasonic plasma's picture quality is better. But there's no replacement for sheer size! If a front projection is a no-go, Mitshubishi is the only game left in town for very large, rear projection televisions. As I said, Mitsu offers screen sizes from 72" up to 92", so keep them in mind if the seating distance calls for that larger size option!
For my money, there isn't much of a better option in a receiver than the Denon 4311 right now. The processing and input options are second to none. And if you go with efficient speakers like the Klipsch, it can even power them just fine on its own. In such a large room though, it's likely that you'll want a separate amplifier for at least the front 3 speakers. Thankfully, the Denon 4311 can easily connect to a separate amp for more power.
I won't throw out a meaningless recommendation for a turntable since that is not at all my area of expertise
Honestly, with acoustic treatments being a no-go, the most important thing you can do is audition, audition, audition! I wouldn't say that there are really any "bad" choices out of the list of brands that your local dealer carries. But that doesn't mean you father won't have a favorite among them! My own personal experience would strongly ward me away from speakers that interact heavily with the room's acoustics, such as the Def Tech and Mirage speakers. But, then again, some people absolutely love the "big" and "spacious" sound that those speakers create, especially in very large rooms where the walls are far enough away that they can really "breathe", which basically just means that the reflections come from far enough away that you brain has enough time to tell reflections from direct sound
So audition speakers like crazy, and audition IN THE ROOM if at all possible. You're not going to be able to "tune" the room to the speakers, so you'll have to be careful to pick speakers that "play nicely" with the room...and with your father's tastes!
Hopefully this will be helpful. I'd say the Denon 4311 is a fairly easy pick. I'd also say a 65" Panny plasma is a fairly easy choice unless the seating distance demands a larger screen size, in which case Mitsubishi is pretty much your only option. Go hog wild on the subwoofers, because that room size is going to gobble up bass! The speakers are going to be all about personal taste. But don't dismiss internet brands out of hand - I think the Aperion Verus in particular might be a real winner in your case
