Confused...not satisfy with my system :

Avico , I hope you didnt read my post as a suggestion for you to get a new preamp.My preference happens to be for tubed preamps.Your last post indicates that you may prefer tubes as well.I will say that matching a tubed pre to a SS amp is not as simple as it may seem.Also the sound that you dislike from your amp may lessen but will always be heard.
If you do want a change and are buying NEW then visit your dealer(s)and try to have a home demo.If this cant be arranged then read everything you can from the credible posters here and try to find a dealer that has a product that interests you on display.
Only you can decide what is best for you.
Best of luck

Avico,
For a warm sound I suggest conrad-johnson, Cary, or the aforementioned Air Tight though they are harder to find. I would also recommend the brand I currently use, Deja Vu Audio a small custom builder, but their stuff is nearly impossible to find. Plenty of good choices though, what's your budget?

Avico, you said that you have tried power cables and did not hear a difference but you did not say what power cords you have tried?
Respectfully,if you have not tried the ones I've mentioned then I think you are doing yourself a disservice.
I too use to feel powercords didn't make a difference until I had the opportunity to hear really good ones!
The biggest mistake many audiophiles make(and you can tell by the responses to this thread)is throwing more money at components when the biggest problems most systems incur that make them sound dull and lifeless is EMI/RFI,power conditioning and vibration control.
Having good powercords and a good power conditioner can improve a system dramatically! without changing components.

A Tube amp or pre-amp will not help you in increasing bass for sure. Tube amps do not have the high damping factor, so they cannot control the movement of the woofer, which results in poor bass.

If you are happy with the midrange and high-frequencies of your speakers and system; it is better you buy a musical subwoofer.

Sonus faber Extremas are inneficient and very difficult to drive because they used series crossovers with no caps, only inductors. The bass inductor dissipates so much power that it has its own heatsink at the back of the speaker enclosure.
You need muscle amps to push them. IMO no tube amps should apply, except for ARC's and McIntosh's top models using the 2 ohm output tap.
Look for an amp that will consistently deliver 200 W into 4 ohms or less. They should mate very well with Gamut D200 or McIntosh MC402 amps.
Here is the original factory blurb:
A "high technology" speaker, Extrema was designed with the aim of handling high dynamics with the lowest possible distortion. It is the first speaker without capacitors in series with the signal (sine cap). It cannot be purchased without commitment because it demands absolute excellence in both the partnering electronics and the installation. The need to calibrate this speaker is paramount if its talents are to be exploited. The cables used must harmonize with the various elements of the system: source, amplification, speakers and environment. .....
BTW Sonus Faber's current speakers are much easier to drive.
Good luck