I not only custom design and engineer custom home theaters/rooms for a living, but I've extensive hands on experience with all the equipment you just mentioned. Actually, the Dynaudio pieces illude me a bit in terms of specific models however. Never the less, if you want truely top calibur surround results from your system, may I suggest the following points of consideration...
One, you have some nice equipment you mentioned, as equipment goes, to deal with for some good sonic results if you do it right!(?...I'll explain). Two, if you want any of this stuff to sound fantastic (not knowing your experience), you should definitely spend lot's of time getting the set-up right in that room! (including seating/acoustical considerations, etc). The room/set-up being at least half or more of the sound, this is of critical concern if you expect to get world class sound from ANY equipment!!(experience is extermely healpful here) Also, how big is you're room!?...this is very important to consider for equipment choices!
But, As far as you're equipment choices for your situation, I DEFINITELY concur with the previous votes for MATCHING speakers all around!!! (at the very very least the front 3) You're wasting your money/effort in achieving any semblence of a great surround/sonic experience otherwise.
The Deal with the Thiel 3.5's you're using, is that they may sound potentially nice and all on their own, but you can't get a matching center for the things!!! Only if you find a 3rd 3.5 can you get a seamless/believable sound across the front. (this probably won't work if you have a TV instead of a projector screen). YOu might get away with Ok results(but not the best) if you use em for rears (or second 2 channel only system), but I'd do others for best results in majority of set-ups. (in which case, sell the speakers or move em!). The Thiels, as with the others you mentioned, are also are a bit laid back, low sensitivity, and thus are a shade uninvolving for proper "cinematic" pressentation really (the antithesis of what you should hear from a great surround system) Higher sensitivity/more agressive speakers will your speakers won't adequately handle Dynamic Digital movie tracks "full range"! You'll need to cut em off at 80Hz or bellow, not taking full advantage of the monitor.(If that Krell had adjustable bass mngmt, you could cut em off at around 50-65 hz for much much better results, leting the sub(s) do the bottom). I've gotten very good results however (some compromises) using Thiel 2.3's and MCS1 center(same drivers) w/power point rears, using all Krell HTS and 250a amps!! While not maximized for absolute best bass managment choices, running all full range except the rears, w/additional sub(s), the result were very very detailed, pretty descent dynamics, and very enveloping! This system desperately needed some better bass managment flexibility, and the Aragon Soundstage proved much better option with the lower crossover points accessible! *(this takes the lowest bass off the speakers, and let's a dedicated powered sub handle the harder chores for way better results).
If You stay with a similar set-up of "full ranger's" all around with that Krell pre/pro, may I suggest an outboard Bass managment crossover by the likes of Outlaw audio! (this will have absolute minimum sonic degredation, with superlative dynamic benefits for HT!!!)
My suggestions, considering you get your 3.5 Thiels out of you're system (or front), I think you'd overall like the sound of what I just mentioned for HT dubties if you like that sound! The Ariels and Dynaudio's are all lower sensitivity speakers as well ,and ultimately prove to be about the same dyamic league as the Thiels!...all with similar results. The B&W's are a bit more sensitive, but ultimately these are all music speakers, that just won't maximize the HT experience as well as other choices to be a bit critical. If you do do get something like the B&W 803's, Biamping them will greatly add to the dyamics of the speaker however!.
Dedicated HT speakers will have a decided advantage for pressentation, dynamic focus, inteligibilty, and less room interaction!(coloration).
If you wanted to stay with the Krell amps and pre/pro, I'd suggest considering something like Wilson Cub II's if you could afford em! 3 of these very high sensetivity(94db!) Ultra HIgh end resolution monitors would be tremendous!!! Also Powered NHT VT3's and similar work extremely well if you got good room size to deal with. Triad Platinum's, Dunlavy's, Revel Gem's, work very well also. Getting into THX dedated movie speakers leads you down an "HT only" type of speaker that's not "house music" friendly however, and you're probably not looking at that option...? (If you notice, all the high end writers used dedicated HT speakers in their surround systems for a reason!!!). Other chioces to consider would depend greatly on you're room size/set-up. Whithout that info, it's hard to recomend speakers to a given room.
Anyway, a bit long winded but the speakers are of ut most importance to consider right now for you, especially depending on what your room situation is! Get me this info, and I'll throw some more suggestions your way.
You're proabably alright with the Krell chioces overall, and I'd concentrate on what you're going to do for speakers. Those will have the biggest sonic impact on your overall sound, as far as equipment goes. So get that right, for YOUR room, and you'll be way ahead of the game. As a rule, Diappolito, higher sensitivity, or even powerd/active speakers will tend to have strong advantages to maximizing the sound the mixing engineer intended you to hear with movies!!! The problem/challenge with most commercially available home audio speakers is that they're not designed to properly take advantage of what's capable from a strong dynamic movie sound track...they're usually designed to play some nice lower dynamic music only stuff! Going the route of speakers that do what good THX type speakers will do, and better, will get you better results overall! There's some very very good non THX high end choices to consider out there butj, again, depends. So, tell me about the room, and I'll make some suggetions. Audioalexander
