Mcintosh C2600 preamp tube upgrade

Thank you for all your assistance!

Update...I've installed the Gold Lions and right out of the box there was a SIGNIFICANT improvement! To my ears the mid's and base are the most noticeable. 
Hard to believe a little over a hundred bucks could make such a dramatic improvement. 
Looking forward to listening after I hit that 200 hour mark!
I appreciate all who helped.

For my C2300 I used Gold Lions in line stage and Telefunken ribs in phono stage.  I have replaced my phono stage tubes with the Mc brand since I now have an external phono stage.

The C2300 enjoys a great reputation. I hope time will put the C2600 in the same positive light. 
I only upgraded the line stage because I only have CD player for source equipment.
Im curious about your thoughts on burn in time. Some say as low as zero hours  just warm up for 10-15 minutes prior to use, others say as high as 200 hours.

The input about the tubes is great, thank you everyone.  A couple of further questions about the 2600.  Does anyone know if the tubes are utilized when going through coaxial or optical inputs vs the balanced or unbalanced inputs?  I clearly hear a difference between the various inputs.  Also, are you enacting the tone control on your inputs.  Again, I hear a difference.  My components are the C2600, MC302, Martin Logan Summit X speakers and a Marantz SACD player.  Any thoughts / guidance is greatly appreciated.  
Thank you!