With a room that large, you really need more bass IMO. Bass is not to be underestimated in the overall scheme because it does much more for soundstaging and resolution than you might think. It is the foundation on which all else is built - and you know what happens to a house with poor foundations... The biggest upgrade in overall sound quailty you can make today would be to get bigger speakers or a subwoofer. Especially with 804s. I really like those little speakers but to get much bass out of them, you have to really whip 'em hard. The latest 804S is not as bad as the N804 but even still, I think they get overlooked by many because they are rarely used in a room small enough for them. Their bass remains tight and guarded.
Now, having said that, comparing a 252 with 2x275s is very interesting. I personally haven't heard 275s in mono but I have chatted with a couple guys here who use them that way, and I briefly had two 240s in mono (I only have one now).
If you don't mind replacing the big tubes once a year and the little tubes every other year (not very expensive), can handle a lot of heat in your room, and don't run the risk of a child or pet breaking tubes, then a pair of 275s gets my highest recommendation. This arrangement will allow them to handle the low impedences of your speakers much better than a single 275 would and give you lots more power and headroom which your amps, room and speakers need to sound their best.
The MC252 is the more practical choice here because it gives off little heat, is much more compact, has more power, has a larger damping factor, and has a much lower price tag. But if you only really care about the sound, you have to go with 150W of tube power.
However, you can't just go out and buy a pair of 275s and then use a Rotel preamp with them! :) Remember that a stereo is a series chain and so only sounds as good as its weakest link.... I would suggest that you get one 275 and a C220. Down the road a bit, you can add the second 275. Two 275s will sound much better than one. This is one of those rare instances when 1+1 = 4.
This is an EE geek technicality but I don't know why McIntosh has "mono bridged" on their website because this is incorrect. The 275s are actually "mono parallel" which is much better than bridging for modern speakers. The difference is that parallel halves the output impedance whereas bridging doubles it. So you get higher current in parallel and higher voltage in bridge. Power is voltage x current so their ratio can be either for a given power rating and impedence.
Either way, you will get much more bass out of your speakers with these McIntoshes than you've been getting with your Rotel. I am sure of that. But seriously consider a sub at some point, or at least a home demo of one, just to see what you think. You might be surprised at how much you can improve your Rotel simply by adding a sub. It still won't come close to fancy Mcs but it will bring you a whole new level of enjoyment in the meantime.
Arthur
Now, having said that, comparing a 252 with 2x275s is very interesting. I personally haven't heard 275s in mono but I have chatted with a couple guys here who use them that way, and I briefly had two 240s in mono (I only have one now).
If you don't mind replacing the big tubes once a year and the little tubes every other year (not very expensive), can handle a lot of heat in your room, and don't run the risk of a child or pet breaking tubes, then a pair of 275s gets my highest recommendation. This arrangement will allow them to handle the low impedences of your speakers much better than a single 275 would and give you lots more power and headroom which your amps, room and speakers need to sound their best.
The MC252 is the more practical choice here because it gives off little heat, is much more compact, has more power, has a larger damping factor, and has a much lower price tag. But if you only really care about the sound, you have to go with 150W of tube power.
However, you can't just go out and buy a pair of 275s and then use a Rotel preamp with them! :) Remember that a stereo is a series chain and so only sounds as good as its weakest link.... I would suggest that you get one 275 and a C220. Down the road a bit, you can add the second 275. Two 275s will sound much better than one. This is one of those rare instances when 1+1 = 4.
This is an EE geek technicality but I don't know why McIntosh has "mono bridged" on their website because this is incorrect. The 275s are actually "mono parallel" which is much better than bridging for modern speakers. The difference is that parallel halves the output impedance whereas bridging doubles it. So you get higher current in parallel and higher voltage in bridge. Power is voltage x current so their ratio can be either for a given power rating and impedence.
Either way, you will get much more bass out of your speakers with these McIntoshes than you've been getting with your Rotel. I am sure of that. But seriously consider a sub at some point, or at least a home demo of one, just to see what you think. You might be surprised at how much you can improve your Rotel simply by adding a sub. It still won't come close to fancy Mcs but it will bring you a whole new level of enjoyment in the meantime.
Arthur