Amp vs. preamp

Hopefully, your expertise can help me out. I can not stop upgrading and i'd been thinking about this for some time. I am relatively new to this hobby and have heard many things regarding amps and preamps. What is more important in the overall scheme of things for home theater and music. The amp or preamp assuming you have really good speakers. Would you guys invest more money into 5.1 processor or the amp? Seeing a lot of these used high end gear in reasonable prices is so tempting to upgrade. I use my system for both music and movies. I also realize room acoustics makes a big difference but i will worry about that later in terms of treating it.

1) Will there be a noticeable difference if i was to step up to a used krell preamp vs. my rotel 1068

2) Or use my rotel preamp and get a better amp.

If the difference is considerable, i might go in that direction. Or just be happy with what i have. Im using revel performa speakers right now.