Confused...not satisfy with my system :

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

I tell you my experience, require a power Extremely high power and excellent quality, and combine with a wire handle cran amount of current and of good quality, I to mine the probe 1 with a Krell KSA-50S and the sound was really unfortunate that gave, now when you buy the Krell KSA-300s is another world, I realized there that have absolutely crosover current applicant, in short all the electronics associated with these speakers should be of high quality, in order to maximize the enormous potential of a once achieved, is obtained to get the most complete musical nirvana!
Greetings Adrian

A top tier tube pre amp will most definitely increase and articulate the bass presence.

Adri is on to something,believe it or not--Some years ago I heard the Krell 300I integrated and matching Krell CD player with Sonus Faber bookshelf speakers and Audioquest cables. The sound was warm, incisive and exciting at the same time.
BTW to me Krell and Arcam are in the same boat soundwise, more or less..That is, incisive and dry, wth a wide dynamic envelope.
Maybe this type of electronics synergizes with your warm sounding speakers and neutral sounding cables.