Yes, 60db gain for the RR2150 is up near the top end of phono preamps I've seen and I agree you've probably maxed out the volume achievable with your current setup. I've always felt the greatest gains in sound quality occur by upgrading the ends of the chain, that is the speakers and for vinyl playback, the cartridge. Speakers are a big investment so the easiest item to replace is the cartridge. I think you'd find the Denon DL-110 or Grado Gold nice upgrades from your Sumiko. The Denon will have a more detailed presentation while the Grado will have fuller bass and both are just a bit more than you suggested you'd spend on an outboard phono preamp. It might be something to consider.