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