I think a high quality sounding preamp can carry a mediocre amp and visa versa. But without question you will want to eventually upgrade any other inferior component(s) to get the desired sound you are ultimately seeking. I would tackle the preamp first since its job is the toughest and it is one of the hardest components for a manufacturer to get right. To find one that sounds decent within a certain budget can be difficult but not impossible.
A few years ago I owned some B&K components & liked them but found out that some of their models stand out more so than others in terms of sound quality. That would include some of their older gear.
A few years ago I owned some B&K components & liked them but found out that some of their models stand out more so than others in terms of sound quality. That would include some of their older gear.