Hi Gareth
ATC loudspeakers for also used for mixing/mastering in studios, which is where this British company started out. They have quite a wide range of passive and active loudspeakers, all with one aim - to produce the most accurate reproduction possible. They will supply any of their paired loudspeakers as singles, so you have a choice between a 'matching' centre and an identical centre. They're all sealed cabinets (like studio sub/sat systems), so placement isn't an issue.
One thing to mention about surrounds. The type of rear speaker is purely preferential. Dipole/tripole speakers can be used to spread sound, but studios, when mastering movie soundtracks, use direct firing (monopole) loudspeakers, which are the same as the front L/C/R. They use these to accurately place sound effects, which can be recreated at home when using monopole loudspeakers. With a 7.1 system, I prefer monopole all round - usually, dipole is recommended at the side and monopole at the rear, but I've never understood this as sounds passing through the back speakers will sound different. I currently use a 'diffused' rear 7.1 set up, but I'm looking to move to a completely monopole set up as it will sound more accurate.
While I agree hi-fi and AV speakers sound different as it's something I've always advocated, but there have been some remarkable improvements in speakers recently from the likes of KEf and ProAc, and I'm sure we're about to see oypthers follow suit. I now feel that products from ATC and KEF possess certain qualities as those of AV speakers. ATC are just so accurate and neutral, and KEF's UniQ driver has such a wide dispersion, that these manufacturers produce the best hi-fi designed loudspeakers that work extremely well with AV. The ATC's do take a bit of driving (although your 82 will be up to it), but will reward you with a far more accurate reproduction than your current set up. you could take a look at the SCM11's all round, with either the C1or C4 (recommended) subwoofer. What you use all round just depends how accurate you want your system.
I've not done direct comparisons yet, but KEF's new Q series is so good that I think they'll be competing with far more expensive loudspeakers when it comes to AV systems. their single point UniQ driver is perfect for anyone who are in close proximity to the speakers - the close you are to a conventional loudspeaker, the more your aware of the bass and treble coming from two different points. This also helps give better image placement - when the full frequency spectrum is coming from one point rather than two, the imaging and dispersion abilities of the loudspeaker ar greatly improved. You could take a look at the Q100's or the Q300's, again, with the same speaker as a centre. As for subs, if you can afford the MX350 or ATC C4sub, the KEF Reference 208 is worth a look - a stunningly clean sounding sub that reaches deeper than the other two if I recall correctly. Obviously, you can also look at other manufacturers subs too if you felt the 298 was too big.
If this isn't tempting enough, there are new products on the horizon from Ken Kreisel, who is currently launching his new company in the US, initially supplying products to studios, with products to follow in the UK next year. As the founder an designer of M&K, he's entering the market with all new designs which should shake up the domestic AV market.
One hi-fi loudspeaker manufacturer is currently working on some dedicated AV speakers at the moment, which I'm extremely interested in - I'll bring news of that when the time is right, as it's early stages yet.
Obviously, your best bet is to arrange a few demos, and all the better if you can compare directly with your speaker package so you can easily, appreciate the benefits.