The room is the most important.
After that its making sure you have a good source. Seriously- if your source(s) aren't doing the job right it won't matter how good your amps and speakers are- they can't make up for lost or distorted signal downstream!
After that its making sure you have a good source. Seriously- if your source(s) aren't doing the job right it won't matter how good your amps and speakers are- they can't make up for lost or distorted signal downstream!