Power Amplifier Longevity

Hi All, 
I am venturing into the separate component world and was wondering how long a good power amp typically lasts.  I may have access to some older Lexicon CX and LX series amplifiers.  However, since they are discontinued and nearly 20 years old from what I understand, should I be concerned with how much longer they will last?  If they do need servicing, is this something that is available at a reasonable cost?  Or should I invest in newer equipment?

Budget is a concern for me which is why I am interested in these older (higher quality) amps at a reduced price versus spending the same amount on something newer, but lower quality.

At this time, I have a Marantz AV8802A and Vienna Acoustics speakers. 
Main L/R - Mozart Grand
Center - Maestro Grand
4 Surrounds - Waltz Grand

I thank you in advance for any advice provided on this subject.

One last thing Brian339. You mentioned you might get height speaker for Atmos later. If you do not want to add the expense for the Atmos amps right now you can upgrade and add them to the Emotiva box later, You do have to send it back for them to add the amps. The amp box has seven amp bays. You can buy a five channel amp in a seven bay box for expansion later. The last two bays would have lower powered stereo amps for the heights/Atmos. Due to shipping cost just have them installed now so you are ready. Worst comes to worst you can power a second room or some out door speakers for now until you decide what to do about Atmos. The Marantz receiver can do all of this without breaking a sweat. 
  iv'e bought a used 1990's arcam delta power amp, sounds great and looks mint  .if i   h e a r   a bad sound than i might worry about caps. it has no moving parts and if it's a quality piece usually it's been well taken care of,if not than after 30 years you will see signs of abuse or humidity.if it looks good and mainly sounds good don't worry about it. lexicon's are a great  choice and sounds way nicer than most of today's amps and will pair well with modern dac's preamps and speakers.go for it.
I'm with Erik. No AV piece made more than a couple years ago is a good bet for longevity (excepting Theta Digital).  The Anthem would be a nice upgrade in sound quality over the Marantz, as well.`One of the most disastrous adventures upon which I ever embarked, as far as my marriage is concerned, was me trying to repair my aging Conrad Johnson PV 5. I didn't think to fully test the transformer until after I'd replaced all the caps and several other components. I personally, will never buy used again. The risk is much higher than people think and the opportunity cost is huge as well.
ditto others, it is said that caps last ~20 y, but that is average, of course....initial quality of caps, how hot the amp runs(ventilation), and amount used, of course, all play a role....certainly they can last longer, but when the amp starts having a hum, they are going......also, humidity can play a role, as restistors, as they heat and cool can crack with age, and if humidity gets in there, I think that also contributes to shortening lives....