To Tube or not to Tube, that is the question

I've been building a collection of hifi equipment with an ear to sampling the major families of tech and their characteristic sounds. One thing I don't have is a tube amp, unless you count my Rogue Sphinx. I like DIY if the final product is of good quality and design. I'm not averse to used either. Budget range is $1000-2000.

Can anyone suggest a tube amp, either power or integrated that would bring a nice sound flavor to my sandbox and not break the bank. OR do you think the Sphinx and the Pass amps pretty well serve up most of what is to be had in terms of tubey goodness and maybe this is not a worthwhile venture?

Here is what I have got in the way of speakers to play with:

And here is the current line up of amps:
Rogue Sphinx     
ClassD Audio Mini Gan 5    
DIY Firstwatt F6    
DIY Pass ACA (2)    
Onkyo TX-6000 Receiver    

Thanks in advance for your opinion.