Hello guys I have a question for you. I play in a very loud band (2 guitar with marshalls) and I have a SWR SM-900 but I can't get loud enough. I need more power and I'm deciding to buy a QSC PLX1804 or Yamaha P7000S. I will use the SM as preamp. My question is, does this power amps effect my sound & tone or just give me power?