I would like to run a five channel amp off of my yamaha 5590, but it does not have preamp outs. so somebody told me i could use a line level pre amp converter from a car audio store. If this is true will it be worth my while to try somthing like this or will the sound quality suffer, I know all the audio stores will tell you line levels converters suck but the fact is I know they tell you this just to sell you a new head unit. ps I love this receiver it has just about all the features I wanted, and the processor sounds great I think it cuold benifit from more power. please help
Can it be done? Yes. Will it sound horrible? No. But it definitely won't be a good sound. Your Yamaha must be pretty old to not have line-level outs.
Here's why: If you convert speaker-level signals back down to line-level RCA outputs, you're introducing a lot of distortion because the waveforms of the signals (and all the signal's flaws)have been amplified. Those flaws don't go away if the wave's amplitude is reduced.
Here's a perfect analogy: Take a few lines of type to a photocopier. Enlarge the page to 200%. Then take your new output and copy it again at 50%. Is the result as sharp and crisp as the original? No way. Not even close.
It's just not a very clean signal at that point. I've used this process with a subwoofer (when the receiver has no line-level output), but that's only with very low frequencies that wouldn't be as prone to noticeable aubile distortion. Even then, it's an absolute last resort. I definitely would NOT do it with higher frequencies.
Another thing: If you like your Yamaha's processor (and I'm assuming you mean surround effects), those will be gone if you add an amp in the way you describe. Why? Because you're only feeding it main left and main right signal. The rest would be gone. Alternatively, are you actually thinking about sending all five speaker leads out to the new amplifier? Yikes. That ol' Yamaha must be made out of gold or something!
Even if this all would work (and TECHNICALLY, it does), remember if you accidentally turn up the volume knob on your Yamaha, you'll be cooking the signal big-time (and probably overloading the amp).
Purity is everything. Consider a new receiver and go the direct digital route: Fiber optic cable or digital coax.