Tony, your little tweety bird is not wrong but like all hear say inaccurate.  I've had in my home the Nuforce, CIA, Linear A, Art Audio, Pass Lab, Krell + others.  Pre-amp wise, I've had the N.E.W, Modwright, tranny passives (aka MusicFirst type) and of course the DaCT pot.  Back home (oz) I'm also familiar with various passives (some DIY using vishay resistors), and some big names like Halcros, CAT, etc..  :MILD:

So...just my experience based on kits I've tried. But you're right, no long term AS experience.  :SLEEP:

On the other hand, I can highly recommend a tranny passive.  Or a much cheaper option, building a pot into the (valve) amp - the downside is more than acceptable. 

I was looking for a SET 300B sound with more oommpph... (don't start this one tricky pony thing ... all been said before...tiring ...) and I expected the Linear A would be the ticket.  But it wasn't.  Firstly, it sounds NOTHING like a SET/300B.  Secondly, even if I accept it's not a SET/300B, the sound (with the pot) does not emotionally touch me...it can come across lean and mechanical. 

Several changes since has significantly improved it but still work in progress.