I got these tips from audio afficionados:
1. In amp, knowing the "era" it is made will give you a glimpse on their sound character. Sabi nila, 70s-mid 80's are more of the "warmth" or "tubey" sound. These amps are on the "lush" and "thick" midrange. Come new millenium, the fad goes for being "neutral" and "detailed".
2. Ung isa namang friend, his though in equipment matching is based on era din. Rule of thumb niya is to match gears that are made in the same era para madaling mapatunog ng maganda. Similarly, he believes that gears are made na bumagay sa "uso" nung panahong itoy ginawa, thus, he easily match gears of the same era. Surprisingly, magaling siya mag pair ng amps and speakers.heheh