The sensible conclusion is that when you replace any part of a system, you spend some time acclimatising to how it sounds - different speakers (for example) may sound better with some tracks and worse with others.
Personally I'm wary about tinkering too much with old equipment, and about any part of advice which is given in capitals! And about utterly emphatic advice, given by anyone who hasn't heard all of your kit - the latter part certainly applies to me, and probably to everyone else here.
Don't worry too much about not feeling like you know an enormous amount - just see how you get on - with the sensible caveat made earlier about not going for Motorhead levels of volume from the off.