best tube preamp to pair LM 518ia

This Rogue Audio RP-1 should fit the bill!
http://www.rogueaudio.com/Products_RP1.htm

Ozzy, I'd say less is always more.

Just remember you will still be going through the preamp stage of the 518. Sometimes less is more.

Oz

I was told that even though the amp has an i restated preamp, adding and external preamp will improve quality. It’s hard however reading that the built int preamp uses same tubes than many preamps out there so that’s why I get confused. My ultimate goal in some years is to end up with 2 power mono blocs (was told that is the BEST) or better power amp alone so I said to me to go for a good preamp now but WITH proper phono stage. Otherwise, would gurus recommend going for a phono stage alone and invest in a good preamp afterwards when updating power amp?

Better sound plus a phono preamp. I have heard LM paired with Shindo frequently and very good results.

Why would you use a preamp with an integrated?

I have a LM 518, replaced all the tubes except the 845s with NOS to take it up a notch. Although the 518 has "pre in" , it's preamp circuit isn't completely "overridden' as it is in other integrateds ; might be better served  simply getting a phono preamp. 

Many thx for feedback guys. Inquired about Luxman and is amazing though quite priced... same dealer recommended the LS 100 tube single-ended preamp from ModWright Instruments. Any thoughts?

I don't think any of the suggestions above have a remote control, and no Shindo preamp, which I would suggest, has a remote control either. 

Maybe a luxman cl-38uc? It has a phono section and a remote control for volume

The Precision Fidelity may be too difficult to find! Instead, the Audible Illusions preamp would be a good choice!

How about a vintage Precision Fidelity C2? All tube and designed by Bruce Moore of Parago/MFA/Audible Illusions fame! I owned a C7 and regret selling it! Any of Bruce's tube preamps can be had for a fraction of the price of a Shindo!