Best Way for my TT to reach my Pre-Amp!?

My thoughts right now is just go with a pair of extension RCA cables and see what you think.
I'm betting you will be quite happy.
I had a TT sitting in a similar fashion, it's cable was 18" too short to reach.
I made it work even more down and dirty with a pair of RCA adapter and another regular set of RCA cables.
Sounded PDG to my ears.
Of course that was just temporary and I had a longer phono cable made from the TT to reach.
But my point is before you blow a load of dough just try it.

Greg is correct in that the Marantz is going to be the limiting factor no matter how good an independent Phonostage you put between it and your TT.

Don’t forget you’ll need to ground your TT.   Phono pre will likely have a place to attach the ground wire from your table and so is a good solution to that aspect.  

Gosh thanks everybody. I don’t think I have the time to address each one of you, but I want to make a few points as to where I am with all of this. 

I want to go back and study all of the impedance stuff because it’s interesting and I want to learn. 
I don’t think the Rega P3 has a separate ground wire.

I have decided on a new phono stage because it’s pretty unanimous it will give me better sound as well as solve my short cable problem. In this journey have learned to make my own Duelund interconnects for when I buy a phono stage. 
I either want to buy a Schiit Mani, Atoll P200SE, or tube phono stage which I haven’t researched enough yet.

I am not quite sure why the Marantz is the limiting factor since it’s just a preamp processor and I am using the best amp I have ever heard in my limited experience, using the Atoll 500 to biamp my MA Golds. However, I am not disagreeing with you, I just didn’t think the Marantz was doing very much in the equation. 

Something you may want to consider is the iFi Micro iTube2 connected between your Marantz and Atoll amp. It will provide you some ‘tube magic’ no mater what your source is, including your phono stage. On a whim I picked one up used and placed it between my Yamaha receiver (which I also use as a processor/pre, not sure it could work the same with your 500 or not, as I only use my B&K for the 2 main channels) and ‘vintage’ B&K amp that powers my mains, and am quite happy with it. Quite an interesting piece of equipment, and seems to blow other tube buffer stages out of the water with its quality and options provided per those who have reviewed it compared to others, many that are more a gimmick than useful addition to a system.