Try mastering at different volume levels on different systems. I try to mix at ~95 decibels for only a few minutes at a time, then turn it down until you can barely hear it and see if it sounds the same. If you can hear what you want to hear at different volume levels on different systems, and the overall percieved volume is good, then you have a good flat mix. I used to think spectral analyzers were not very useful, but a good stereo imaging and spectral analisys plugin can show peaks and problems that your ears might not be picking up. When I use to make tracks mostly for vinyl, there were some rules we tried to follow to make sure the record came out nice and loud. Most of them came out louder than was necessary, and I/we generally overcompressed things. I always find problems on different systems with tracks that are long ago finished and released that I want to re-master. I master in headphones (Shure E2), use cheap monitors (Sony NS50s) for arranging. If you have similar music to compare to, listen side by side with your tracks on the same systems at different volumes. Most music can be mastered well with a parametric eq and a multi-band compressor and an exciter/limiter. I don't think it takes any special equipment, I have not found a big difference between software and hardware, except that software can be more flexible.