Which amp would you choose and why - Pass Labs XA-25 or First Watt F8?

The XA25 is the much "safer" choice in that it has much more power and is stable down to 1/2 ohm.  From everything I've read (and I had the XA30.8 paired with similarly spec'd D7's), the XA25 will have better bass and silkier mids.  The F8 may sound a bit more agile but possibly lean in comparison. Your Tannoy's can go as low as 20hz and the impedance dips all the way down to 2.9ohms at 100hz.  I really think you will need the XA25 to drive those Tannoy's properly.  What amp are you using now?

I have the xa25, much more powerful than its rated 25w, especially at 4 ohm dips.  I have an F3 which sounds glorious, but not near as powerful. I’d love to hear people give their perspective on the F8.

These flea watt amps are a niche possession. 
   Get 250-300W min. !!!

 Headroom, the airy effortless sound will be awesome.    Even a 25W amp will clip very easily on average to med-high volume. 
 I learned my lesson years ago, I’m NOT saying Nelson or low watt stuff is bad, NO WAY!

  Having the reserve, and hearing the huge difference with power reserves will make a difference, if and when you want a little bit of volume.  
For a small room, and never wanting to push volume, it will be fine.
if you think you need to jam a few songs, those small W amps will clip!

  250W or more. 
I’ve been through 50, 75, 80, 100,125, 165W amps, once I bought my first 250W+ amp, never have I looked back. 
 Enjoy the music!

i have an xa25 that is coming into its own after a week and there are moments of absolute brilliance.  power and drive with my 86db Harbeths is more than adequate.  Also running a Cary tube preamp.