How reliable is PS audio equipment?

The only issue I’ve had with my BHK preamp is having to replace the tubes at about 5000 hours. 

Whomever informed you there is a 20 year usable life is misinformed.   I have a vacation home with a 45 year old Pioneer SX 828 producing excellent vintage sound.  Usable life depends on the design, especially heat generation and dissipation, the type of usage (pro, home, hours, stress conditions), and the care given to the equipment. I had in the past 20+ year old Krell separates that sounded new  because, suffering from OCD, I had Krell service them every 5 years.  The is admittedly excessive.  Your preamp is well built and low heat output.  I recommend having it checked by a good tech every 10 to 20 years and it will live on past any humans life expectancy.  The limiting factors are parts obsolescence and abuse. 

I have a PS Audio Stellar Gold Preamp, a pair of M700 Monoblock amps, and a Directstream DAC Mk1 (modified by APS Transformers.) In the past I have had a Directstream DAC Junior, and a Stellar DAC. I had one issue with the Stellar DAC (failed right channel); even though it was out of warranty, PS Audio fixed it for free. The Stellar Gold Preamp had one problem when brand new (triggers didn't work), but in all fairness, I was a beta tester on that unit, so some issues were expected. All in all, I have had PS Audio components of various models for about 10 years, and found them to be very reliable. On the rare occasions that a problem did ensue, they were very responsive and great about solving the issue with fast turn around times. I would certainly not hesitate to purchase their products.

The Directstream DAC's are built to last.  We upgrade them currently and are hard to beat at any price. They simply sound awesome with the upgraded nickel transformers and power supply.

I have lots of PS gear now, and have had various PS gear for 35 years...never a single problem...and if I have questions it's always very easy to actually talk to someone...