Paul Klipsch was right - What the world needs is a good 5 watt amplifier

Sensitivity isn't the issue as much as impedance curve. The Pass can handle it because those speakers are it's raison d'etre. A 300B SET won't do here.

Having said that I used 845SET's with Merlin VSM-MM, around 90db with pretty benign impedance curve. I doubt 300B could handle. I once tried for kicks 2a3 monoblocks I had at the time on the Merlins, nice transistor radio sound.

The problem with 5wpc amp is so few speakers allow for it. I'm not even sure my Klipschorns would be happy with less than the 8wpc my 300B amps provide. I was considering 2a3 or 45 amp until I saw a number of less than stellar reviews of the pairing. Khorns  with shallow slope crossovers do have a bit of impedance concern, steep slope and drop down to aprox. 3ohms at 100hz.

I'm not even sure my Klipschorns would be happy with less than the 8wpc my 300B amps provide.

I know some people like low power amps (single digit output) but even at lower volumes higher power amps can work better. I use 25wpc tube mono blocks on my main system and it's enough for me. I have used low power chip amps but they fall far short. I think some are satisfied with what they hear but I assume they my be ignoring the benefits of higher power or in the case of a quality tube amp, they sound more powerful than their low power rating suggests. 

@jasonbourne52 

The Topping PA5 ($349) is more powerful than the Pass amp and has lower distortion. Why pay 10X the money for the Pass?  

I've great appreciation for topping devices and with great respect I think the PA5 wouldn't be able to drive those speakers above 80dbs before it will start clipping. Don't rely on laboratory measurements as the music is much more complex and dynamic and it is not 1 KHz sine wave

I cannot name this individual ( it is not me )....He owns top of the line CJ gear / Avantgarde horns....Based on my very positive recent talks with him about a chip amp I have been listening to, he went ahead and purchased the PA5, AND LOVES IT. He also has gone passive, and is loving his new sound. His words : From warm and colorful, to clean, precise, immediate, snappy, detailed, fast........more truthful to the recording ( whatever that means ). Enjoy. I am loving my chip amp. 

This is so appropriate for me right now. A couple weeks ago I built a $150 K-12G tube amplifier of 8w/ch......I built it just for fun as I like building stuff and the price was right. I had zero intention of ever using it seriously. But then I connected it to my KEF LS50 Metas and Oh My Lord, does it sound great! At up to 80dB in my 12X24X8 heavily damped room it never strains. The sound quality is simply magnificent and I find myself listening to it for hours. I also have a Pass Labs First Watt F5v2 (50w/ch) and a VTA ST120 Dynaco Clone (60 w/ch) and a Yamaha M45 (125w/ch)....And recently I’m favoring the K-12G.....Read all about my adventure with the little amp here... www.rvbprecision.com