So I have Klipsch KLF 20's which are rated at 99db give or take a couple. Many people say all you need with these is a few watts in tube amp and you're going to be happy. I have a 45w Marantz PM6004 which sounds great with these. For rock music it plays them clearly as loud as I want.
That means you have all the power you need. Reread that a couple of times until it sinks in. What more power would get you is louder, not anything else.
So if I hooked up the 300 watt emotiva xpa 2 what differences might I notice at low(65-70db) and moderate volumes(80-85db with 95-100db peaks)?
Nothing at all.
Your speakers are rated for 100dB at 1 watt at 1 meter. If we figure that you are a couple of meters away, you will likely then need about 2 watts to get that volume. And that is about 2 watts for your peaks, not continuous power. An amplifier capable of more power will get you nothing at all, except it will make you poorer from the cost of the amp, and poorer from the cost of the extra electricity the thing will probably waste.
Right now the only deficencies I see with the Marantz are the bass is a bit weaker than I would like but I am not sure if that is a power issue or a function of the gain on the preamp.
It is neither. It is either that you want speakers that produce more bass, or you want to change the tone control or loudness compensation settings on your integrated amplifier.
For example if the amp had a bass boost function it would probably put out adequate bass.
Try using the "loudness" button on the front of your unit. It is not the same, but is a similar idea to a bass boost function (it also will boost some treble, as its function is to make music played softer than natural still have a natural sounding tonal balance; human hearing is very imperfect in this regard; see
this).
Now, boosting the bass will likely mean that you will be using more power. But you already have much more power than you are using, if your statements about the volume levels you want are correct and you are not a ridiculous distance from your speakers. A 10dB boost would mean that you would need 10x the power. In other words, about 20 watt
peaks at your proposed volume.
You will want to shut off "source direct" for this (see your manual). You can also try using the bass control instead of or in addition to the loudness button.
So my question is. If had 300 watts, would I ever even use much more than the 45 I have now if I'm not playing the system much louder?
It would do nothing at all to the sound.
If I had a watt meter what outputs would I likely see with rock music at 90db for example (I know that's not scientific, just a ballpark venture)?
Thanks
Jon
It would be less than a watt, assuming that Klipsch has rated the speakers even close to accurately, and that you are not at some unusually great distance from them. With 1 watt, you should be getting about 100dB at 1 meter, and likely about 97dB at 2 meters, though that will depend on room acoustics.
Now, as ski2xblack indicates, if you had a poorly designed tube amp, then it could screw up the frequency response (and also add distortion), which you may or may not like. I do not recommend it.