Has anyone had success with a preamp with a Marantz PM 8006?

I agree with @tablejockey  however also believe assessment of the improvement to be expected relative to return on investment by purchase of an outboard phonostage would require knowing what TT, arm and cartridge is in use.

@rpppr Again, I agree with @tablejockey.  Your TT set-up out classes the Marantz 8006. That said, with a vinyl system TT is the most important component. Regarding the purchase of an outboard phonostage, would you consider upgrading the integrated amplifier thereafter?