Proper Preamp into Vintage Marantz 2226B… needed?

I really love the sound of Marantz vintage which I  have…powering into my 102 dB Klipsch Cornwall IVs.

But  I saw a video on YouTube, which made me think that I can get even better sound by getting a preamp and running some RCA cables into the Main In area of the Marantz 2226B. I have plenty of sound right now because of the efficiency and the warmness of the Marantz amplifier. Do I gain anything? Has anyone else tried this type of set up and which  preamplifier do you suggest would be a good match?