Best Tube/SS Amps for Harbeth 7ES-3

Hi, I just bought a pair of Harbeth Compact 7ES-3 - beautiful sounded speakers. Very natural and musical.

Now I need to get an integrated or Pre/Power combo to drive it. Budget is about $3-4K new or used. I read the 7ES-3 is easy to drive. Which amp works better with the 7ES - Tube or SS?

What amps do you use for your Harbeth 7ES? How much power output do I need to drive the 7ES to its full potential?

Would a 20 watt per channel tube amp drive the Harbeth?

Now that I've settled on the speakers, I can focus on getting the amps :)

Alan Shaw never said that all amplifiers sound the same. Amplifiers can sound different for a number of reasons. The first is if the input sensitivity is too high, as is all too often the case. This may sound impressive, but what you are hearing is clipping and the concomitant compression. The second potential problem is insufficient power. The requirements can vary enormously depending on room size, speaker efficiency and music type. However, more is always better. Alan Shaw recently demonstrated the M40.1s in Hilversum in the Netherlands (there is a Youtube video somewhere on the web) and the amplifier had big digital power meters so one could see what it was being asked to deliver: at times more than 500 watts.
The third problem is a load dependent frequency response. Stereophile has these very useful graphs of frequency response under simulated real conditions, and the results are sometimes really bad, especially with tube amplifiers. Here solid state is clearly better and often by a wide margin, but tubes are not the only dispointing amps. Some  boutique solid state amps can be almost as bad. This matters, because any deviation of more than 0.2 dB is audible. The solution is a powerful amplifier with a beefy (and hence expensive) power supply. In the absence of proper measurements, you could select your amplifier by weight. The good news is that mainstream Japanese manufacturers all have this under control. If you are looking for big power of high quality, there is little to beat a pro audio amplifier like the 2x250 watt Yamaha p2500s that I recently gave to my son (for use with a Harbeth M30.1), or its bigger family members. The 2x350 watt P3500s was tested (i.e. mesured on an Audi Precision test bench) in a French publication and it was as perfect as could be, and better than many audiophile amps.
As a pre amplifier you could go for a DAC with multiple inputs and variable output (including XLR) like the Pioneer U-05.
The Vinnie Rossi LIO integrated is an ideal match with Harbeth and gets best of sound at every show no matter which Harbeth is being used.
A little over your budget. I upgraded to PrimaLuna Prologue Premium pre-amp and Prologue Premium mono amps  . 70W/ch EL-34 tubes. With 7ES-3s getting plenty dynamics, bass, tube glory without the ripeness that can blur resolution and transient attacks.
I used to own a pair of 7ES3s powered by a Rogue Cronus Magnum 2.  It was a great combo.  I also heard them powered by a LFD and Vinnie Rossi LIO and both were excellent matches.  Also, if you're looking for a tube amp and a step up from something like the Rogue, take a listen to the Leben CS600, it just sounds wonderful.  I was all set to upgrade and buy a Leben and a pair of SHL5+ but ended up going in a completely different direction.  Other amps that many consider a good match include Luxman, Naim, Hegel, Sagden and exposure....just to name a few.  Btw, the best bang for buck in my opinion is a used Hegel. 
I have found that the C7s sound better with more power.  Some say they are dull speakers, but when they are provided with sufficient power they can sound dynamic and agile.  I'd suggest 100 wpc as a good minimum.  So, something like the Cronus Magnum 2 or the Primaluna Dialog Premium HP (w/KT 150s) would be sufficient power from a tube amp.  Harbeths sound quite good with solid state power as well, and there are many solid state integrated amps at 100 wpc and above.  A tube preamp and a powerful SS amp would also be a great match with the Harbeths. 

Good luck!  Scott