Dennis Had Inspire SET with KEF LS50s

I have not, but I think you will find better pairings, especially if you listen at decent volumes. I am sure it will sound very pleasant, but if you A/B'd against against a more powerful amplifier you would hear a huge difference.

I lit up a pair of LS50s last week with a Musical Fidelity a1008 integrated that can swing 75 amps of peak current and it sounded far better than a Primaluna Prologue classic that was driving them prior. It was also a huge improvement over a Bel Canto c5i. You could tell they really responded to the additional power. 

The Kefs are rated for 8 ohms, but they have impedance dips that makes them mate better with an amplifier that can easily handle a 4 ohm load. They are 85db sensitive, which is borderline low. 

On paper it is not a great match, and based on my experience they really do like power. 

I'm currently driving the LS50s with a Parasound A 23, and have used an A 21 in the past.  I thought to use the Inspire as Zone 2 from a Cary Cinema 12 with the A 21 remaining as Zone 1.  It seemed an inexpensive way to try a tube SET amp.  A friend who is very knowledge about audio setups suggests the Inspire damping may be insufficient for the LS50.  I haven't used a tube amp since the mid-60s, although I hear my cousin's Cary 805s several times a year.

I forgot to mention that I supplement the LS50s with a pair of Velodyne HGS-10s and SMS-1 bass manager, crossed at 100 Hz.

The Inspire amps have great drive abilities, a lot better then a 300b SET.  What are your goals?  is this to be your only amp?  For me, I enjoy playing with this stuff.  I like to throw in a SET for a few days, and then go back to my Ref75se.  The great price on the Inspire amps allows me to play a bit...

Technically, Dennis Had's Inspire amps are SEP's not SET's, since they use Pentode tubes, not Triode tubes in the output stage.