I own a late-90's Mackie 1604-VLZ mixer, a late-90's Mackie 1400i power amp, and two Grundorf ST-152 speakers. FYI: This equipment was given to me about three years ago and I have some questions: 1. On the power amp, the channel one input is fine; however something happens inbetween there and the output that the causes the output not to work. It got great reviews all over the web; what do you think about it? Is it worth fixing or should I buy an amp that will not die on me like that? I have a theory for why the output is dead. I have learned that if you have nothing on the other end of the output cable, but still run the gain up on the speaker, that the amp will fry. I ran a dead speaker for a long time, obviously unknowingly. I fixed the speaker and the amp ran great for a while, then the channel died. 2. Is my power amp/speaker compatible? The amp is 500w RMS stereo @ 8 ohms. The speakers are only 150w @ 8 ohms a piece. I know it is bad to under-power a speaker, what about over-powering? Would my potential over-powering be causing the unusually sensitivity of the system to feedback (which is actually another great concern of mine)? 3. Three channels on the mixer are dead, that is, no input signal. Two were already upon receipt, one happened just over a year ago. The mixer sits in a power conditioned, practically sterile control room. What would cause these channel-deaths? I am apt at soldering/working with electronics. Is there anything that I should check out that I could fix on my own? 4. Please comment on my system. Should I trash the amp and buy one suitable for the speakers? Should I fix the amp and buy speakers suitable for the amp? Or, is my setup fine how it is and I should just get the amp fixed? I understand that this is a lengthy post. However, pro audio is a lengthy subject so I guess I am in the right place. Thank you so much!