Upgrading from Thiel 2.7 to Sonus Faber or Focal???

Thank you for the information.  I can handle the 2 fronts if the cabling doesn't take care of the issue.  The Mullards are great tubes but pricey these days as they are becoming scarce. 

@samzx12
I dont have first hand experience but in my research on rectifier tubes (Im currently using NOS Mullard 4 notch GZ34’s) I’ve found feedback that the Phillips 5R4GYS adds warmth to PL preamps.
They are taller though. The cage just touches the top of them but Kevin Deal says that’s how they run them and they are fine

As an owner of Thiel CS2.7 speakers I can understand why you feel 
that there isn't enough bass but It is not the speakers .
Your room and it's treatment will have a lot to do with any speaker and 
as suggested TUBES , yes your tubes play a large part in fidelity 
and frequency range .
I will suggest that you go out and buy pairs of tubes ,
like GE , RCA , Sylvania from the 50's and 60's to hear how different 
each pair can sound and if you start to hear what your looking for 
you might want to try Telefunken tubes .
You'll find mixing tube manufactures can give you the sound you are looking for .
Tube rolling is easier and cheaper than switching out speakers
and more fun .

Robert I may try the 2 front tubes since they have the most affect but not going down that road again with the rest.  Did that with a Primaluna Dialogue integrated amp. Spent a small fortune but yes it is fun.  

Rushfan have you seen the price on the Phillips GZ34? 😬😬😬

samzx12
I apologize for assuming that you haven't tried tube rolling .
My enthusiasm for the Thiel 2.7 speakers is something that I can't hide .
Have you tried a 12bh7 or 12av7 tube inplace of the 12au7 ?
Try asking the question about improving bass response on the Thiel Owners forum .