Mailist to discuss all issues regarding the Digitech GSP-2101 Guitar FX Processor

So my preamp tube has been in there for 8 years.  When is it necessary 
to replace these tubes?  Can I replace them myself?  AKA Pop it open 
and pop them in?  

Any recommendation on what kind of tubes.

And on a random not, I play my 2101 artist through a Marshall 9100 and 
lately I think the power tubes of my 9100 have finally broken in 
because it sounds so friggin good.  I will never be able to own a 
normal head ever again.  Just not worth it.  OK.  That's it.