IMHO, the order would be:
1. Interconnect from preamp to power amp.
(My reasoning is that everything goes through this cable.)
2. Speaker cables.
(Everything goes through the speaker cable too, after it goes through the above cable.)
3. Interconnects from sources to preamps.
(Your source signal should be as clean as possible. Note: if you only run one source, you might want to make this your very best cable.)
4. Power cables.
(This is variable, depending on whether you have dedicated circuits or not. If you do, then having better power cables is not nearly as necessary, IMHO. If not, than power cables, and possibly power conditioning, should be a priority. I have dedicated circuits, so I have not bothered with high end power cables. Fyi: I tried some, and it did not seem to make much of a difference.)
My two cents worth.
1. Interconnect from preamp to power amp.
(My reasoning is that everything goes through this cable.)
2. Speaker cables.
(Everything goes through the speaker cable too, after it goes through the above cable.)
3. Interconnects from sources to preamps.
(Your source signal should be as clean as possible. Note: if you only run one source, you might want to make this your very best cable.)
4. Power cables.
(This is variable, depending on whether you have dedicated circuits or not. If you do, then having better power cables is not nearly as necessary, IMHO. If not, than power cables, and possibly power conditioning, should be a priority. I have dedicated circuits, so I have not bothered with high end power cables. Fyi: I tried some, and it did not seem to make much of a difference.)
My two cents worth.