Aesthetix Calypso Signature to Eclipse

I can upgrade for $3500. 

I changed out the stock 12ax7 tubes for these: 
http://psvanetube.com/wordpress/store/products/shuguang-custom-12ax7-lx-special-edition-pair-low-noi...

So far I haven't noticed a difference, but I'm not sure if there's any burn-in.

 Running dual sub outs at line level plus low input impedance amp 
 will prove fruitless for you and is suicide for any fine tube pre amp,
Try going out with subs at speaker level and find an pre owned Atlas.  

My amp (Sanders Magtech) has 100kohm input impedance.  Is that considered low input impedance?  I'm not sure that I understand your post about subs.  My subs are powered, and I've read that it's better to run them via line out and not through speaker level.

I don't plan to upgrade to the Eclipse version or Callisto.  I can barely tell any difference between my Odyssey Candela ($1500) and my Aesthetix Calypso Signature.

Have you tried your subs via speaker level?
  I think you may be in for a pleasant surprise

No, but I don't always run my subs.  They stay connected but are often off.