From lehmann blk cube to Nova Phonomena with...?

If you already have the power supply, I say just get the best phono preamp you can afford. It will make the biggest difference.

@ Zd542: thank you for the advice, I was thinking myself to get the P75 (due to the ideal match with the cart, as you said), the problem is the cost of the same too high in my country.
BTW, I already own the external power supply for the P5 but I was thinking to get also the Groovetracer subplatter (and the others upgrade).

I've had both of those cartridges my self. Moving up to the 20 will be a big improvement by itself. As far as the phono preamp upgrade goes, I would go a different route.

Its less money, but I would get a DV P-75 phono pre instead. Needless to say, its a good match for your new cart.. Use the money you saved and buy a Rega power supply/speed stabilizer. That should make a much bigger difference in SQ.

Some folks do make upgrades that are questionable, or even go backwards. But the Nova Phenomena is a lot better.

As with any other upgrade process, some will find the upgrade to be worth the extra money, while some will find that an upgrade was not worth the extra money. In the end, it is your money, and only you can determine if an upgrade is worth the money or not.

That said, most here are on the constant upgrade trail, and I suppose they will tell you that it is worth the extra money to upgrade. I rode that train for many years, it wasn't until I dramatically downsized and realized that my system didn't sound much worse that I started to think that all of those "upgrades" I made over all those years, maybe weren't all worth the extra money.