Tony,

Your extra sound level mostly comes from the higher sensitivity rating of the larger 15 DLs. As you probably know, the sensitivity is basically a rating of how much sound pressure is generated at 1m distance when given 1W of input power. Smaller drivers like the 3" satellites typically put out less than 90dB (for 1W@1m) whereas larger drivers like your 15's can generate around 100dB for 1W input. This is more than 10dB sound output for the same signal power input, and subjectively would sound at least twice as loud. It's basically a function of the larger surface area of the 15" being able to shift more air than the smaller 3".

I have not measured the impedance rating of the z5500 satellites but would expect them to be in the 4 to 8 ohm range. Miden is right in warning about the possible impedance mismatch, but your 15 DLs should be okay and hopefully should be rated at somewhere between 4 and 8 ohms. You can check this in a crude fashion with a cheap multimeter. As long as you stay above the minimum rating per amp channel, everything would be OK.

If you attach speakers that are lower impedance than the satellites, but are still above the minimum impedance rating of the amp, this would also be OK and would contribute to the increased sound output level, becasue the amp would be able to deliver more power into the lesser load impedance. As Miden said, just be careful to check things first.

Please consider that this description is very much generalized as there is a bunch of other parameters that also affect the sound output level. But hopefully it is of some use.

Mark

[This message has been edited by batty (edited 03-23-2006).]