Threshold verse Pass Labs how can I justify significant price difference

I'm running currently series one Threshold S500 with the optical bias and Threshold S500 second series as a bi amp config to my JBL 4367. System sounds the way I like it no complains.
Now I've been having thoughts about upgrade amps to Pass Labs 350.5 or 250.5.
250.5 would be in same power range as S500 so my question is since Pass will be priced higher how much better would it sound and is it worth to spend extra $$?
does 250.5 will make so much difference that there is no sense to go up to 350.5? or the only way to get any significant upgrade is to go for 2 of 350.5 and would it be so much better sound than my Thresholds I could justify spending extra $7K!

Can't wait to hear what you guys have to say.


Nelson Pass seems to suggest prolonged "Class A bias" as a positive attribute. FWIW, the Threshold S Series amps were said to be "Class A biased" to 20 % of it's rated full 8 Ohm output per channel. That would suggest that your S 500's  has a "Class A biased" output of 50 Watts per channel. More than the either the Pass Labs 250.5 or 350.5.

I would listen long before I made the decision a Pass was an upgrade.

Also on your list should be Ayre and Parasound.

Ayre IMHO is a much better sounding amp than Pass, and the Parasound may be a significant upgrade just from virtue of being new, withoug the megabuck costs of the Ayre or Pass.

Of course, Bryston too should be on your list.
Above all, your your own ears, and not necessarily the price tag to guide you.
If you want to hear a significant difference, I would forgo the X series class AB amps and go for the XA series class A amps.  And use them for the HF/MF in the bi-amp configuration.
So as far as I can see, I should live alone my setup.
the only reason I would even look at 350.5 is  its looks and appearance.  And since there is no significant difference between S series and Pass X series there is no point for me to spend money. 
BTW I’m aware my amps aren’t the best but I like how they sound and look and I like to stick with Pass design amps.
thank you guys for your opinions 
The thresholds are very nice but the Pass amps have completely different circuitry and you will find significant differences in sound vs the threshold amps.  

I would still keep a threshold amp as a backup amp.  The perceived differences between Pass amps is an entirely different matter.  I would have to hear them in my system to judge. 

However, no contest between the still very good threshold vs Pass gear
^FWIW, I prefer the looks of the S 500 without the distracting glowing meters of the Pass Labs.
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Valid point and all opinions lead me to conclusion to stop improving my setup and start enjoying it.  All doe I always wanted FAT 10 both panels so I just might get it and see if on pre amp stage I could improve situation 
Get the the Pass and find out for yourself. You can always sell it, if its not what you seek. But I am sure you will be wondering what the hell the people in this thread were talking about.
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It sounds like no one posting above has direct experience comparing the two, so their guess is no better than your own.  Hopefully someone who has compared the two will chime in.
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Sorry, not having read enough of this thread, I may be repeating something here. I owned a Threshold S500 and took a peek inside. It was impressive, 'for it's time', I will say that. As well built as it was, there was an issue with the channels being cooler than they should, which is a bias issue. My point here is that to resolve all the issues associated with getting the amp back to spec was not worth the effort. The search went on from there to find a suitable working replacement.
I’ve heard both. Both similar and different. Neither necessarily better. YMMV.
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