I am currently driving 3-HTM12's, and 6 JBL Control 226's with a Denon X4300 rated at 125 watts per channel. It really does a pretty decent job, but would like a little more headroom for Blu-Ray concerts. I am thinking at least a solid 200 watts per channel to drive at least the HTM12's. I have been looking on ebay and there are some good deals sometimes on used 7 channel, and 3 channel HT amplifiers. Looking at brands at around $1k such as Crestron, B&K, Lexicon, and Monster Power.
What would you guys do? There have been some 7 channel amps going for not much more then a comparable 3 channel amp, maybe $200 to $300 difference.
Is this the HTM12 you have? If it isn't your speaker then the following may be interesting, but it doesn't really apply to you.
http://www.diysoundgroup.com/featured-for-mg04a00409/ht-12-kit.html
The specifications for the HTM12 list it as having a voltage sensitivity of 97dB SPL. Since the impedance is given as 8 ohms then the power sensitivity would be 97dB SPL at one watt. That makes the HTM12 a very sensitive speaker.
A 100 watt input would give 117dB output at one meter. Even taking away say 5 dB for distance that's 112dB SPL, even minus 10dB is 107. Reference is 105dB at the listening position so it's hard see that you need over 100 watts for these speakers, and likely less.
The JBL Control 226's evidently have a voltage sensitivity of 90dB SPL into 8 ohms using the lower listed value number from the JBL webpage. Again 90dB would be the output with one watt into 8 ohms.
100 watts into the JBL's would give 110dB SPL into 8 ohms at one meter. Subtracting 5dB gives reference output of 105dB SPL. Subtracting say 8dB gives 102dB. To get to 105dB would require 200 watts, with this 8dB reduction, which exceeds the 150 watt rating of the Control 226. The Control's just won't keep up with your main speakers if really pushed, again based on the specifications. Keep in mind that the output of most speakers suffers from compression at high power input levels, that is, SPL output rises more slowly with each increment in power input, than at lower levels. The surrounds require a lot of power to reach reference, and depending on your listening position, may not make reference.
Often posters on this forum report watching moves at -10dB vs. reference which would reduce the power requirements by 90%. Evidently, for at least some of your listening, you don't belong to this group!
While it may seem odd, if you do listen at reference, and the material you listen to has quite a bit of energy in the surround speakers, then the limits you are hearing may be coming from the surrounds during peak output periods, or a least the surrounds are adding enough load on your AVR that the output of all the speakers is limited.
Given the above it makes sense to add an external amplifier. External multi-channel amplifiers aren't supermen. Unless you get something like an Anthem P-5 (expensive) that has separate power supplies for each of its five channel, the power output, actually the current capability of a multi-channel amplifier, will still be limited with all channels driven close to their maximum.
Given the above, an amplifier such as the Outlaw Model 7140 would be a reasonable choice at the bit over $1k. It supplies 140 watts into 8 ohms and 200 watts into 4 ohms, into 7-channels. I'd be tempted to connect the Model 140 to the L,C,R and two of the surround channels. 140 watts into the L,C,R will provide a very high SPL. 140 watts into two of the surrounds will take them to their maximum SPL input. The Model 7140's ability to drive 200 watts into 4 ohms loads will cover portions of the frequency spectrum where you speakers drop below 8 ohms. Using only 5 of the 7 channels of the Model 7140 will essentially allow it to loaf along, even when providing maximum output on the 5 channels. Your AVR should be able to drive the remaining speakers, if not, then connect more 7140 channels or get an additional external amplifier.
An external amplifier with a higher power rating will be unlikely to give you a higher overall SPL level than the Model 7140. Your surrounds will be driven to their limits by the 7140 and your AVR. The HTM12's are rated at 500 watts maximum, but compression and distortion will be come significant factors before this power input level is reached. Also the difference in output between 140 watts input and 500 watts, even without compression, is something like 5dB SPL. A 300 watt amplifier will only give 3dB of added SPL output, a 200 watt per channel amplifier around 1dB or so of added output, which at above 105dB SPL is unlikely to be noticed.
