Mcintosh C220 pre

I purchased a C220 yesterday to run my MC352 and have a question or two. How do you burn this unit in properly? Do I leave it on with a CD signal feeding it for a few days? Can I leave my power amp off? What can I expect in terms of sound when it is broken in? Will there be more detail, better imaging etc??? Also should I have some spare tubes around? If so, which tubes do you recommend that could add a bit of upper mid detail? (I have read the C220 can be a little lean in dealing with those frequencies)

I look forward to any opinions!!!
Thanks........