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

I agree with both of you.  I just purchased a [aor Klipsch Heresy IVs and need to wait "for the dust to settle" to make another significant  purchase.

@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?

"Garrard 301 (Oil bearing) turntable with an SME 3009 non improved arm with a Ortofon 2m Brown Cartridge."

Spend more money and get a "better" main amp and phonostage.

The table setup warrants a substantial amplification upgrade.

I currently have a Garrard 301 (Oil bearing) turntable with an SME 3009 non improved arm with a Ortofon 2m Brown Cartridge.

I previously had a PM 8006. It is known for having a good built in MM phono stage. I d experienced a nice improvement in vinyl playback by adding a Rothwell MCL step up transformer and using an MC cartridge. 

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.

"I listen to primarily Vinyl and I was wondering if anyone uses a phono preamp.  Just curious to see if anyone has had any success. "

It appears the OP is masking if an outboard phonostage is "better" than his built-in.

The answer is for his particular price point Marantz, probably best just enjoy what you have, or look at something  like the Schiit Mani for $150. SQ improvement might not be that dramatic assuming the Marantz built in is decent for a price point appropriate table/cart setup.

Oh, I probably will not.  I listen to primarily Vinyl and I was wondering if anyone uses a phono preamp.  Just curious to see if anyone has had any success.  I am content with what I have right now.

Why would you want to use a separate preamp with that?  It has its own preamp built in.  The Marantz preamp section usually sounds pretty good,  unless you want to try tube preamp for some flavor.