Would a Pass Aleph 5 be able to drive Thiel 3.5 ?

I have a Threshold FET-10e pre-amp and a pair of Thiel 3.5 speakers. Currently, I am using a Bryston 3B-ST. My source is mostly CD based using a Esoteric P-500 transport and a PS Audio Ultralink II. I plan to purchase a Pass Aleph 5 to replace the Bryston. Would this be a good idea ? Would I get any improvement ? Any help on this would be greatly appreciated. Thanks.

Not adequately. I've owned both, though admittedly at
different times. The Aleph 5 is very musical, but
current capability is not its strong suit. The Thiel
3.5 needs lots of power. I'd recommend something like
a Levinson 23.5, or a Bryston 4BST which can provide
the horsepower necessary for a satisfying result.
pass aleph 5 is rated 60W/ch pure class A. The way it drives the speakers even with low efficiency it would seem to me that it works at least twice the rated power. I'm not realy sure if it does switch to B after it riches 60W/ch but it no worse driver than 3B-st. The musicality and mids are very close to tube performance so I guess you should only gain in performance but you might notice that your room will be much wormer since this amp is getting real hot.

Good luck!
Of course your room and desired volume level are paramount in this regard. Your pre-amp out put should be considered too. Thiel recommended 50-250 watts (as rated into 8 Ohms). As they are a steady 4 Ohm load I prefer to think in terms of 100-500 Watts into 4 Ohms. The 3.5's use and equalizer to bolster bass response. This can put an added burden or your amplifier. The answer to your question is yes but more power would be better. I would recommend at least 200 Watts into 4 Ohms. By the way, I think Pass would sound very nice with these Thiels, but some of the early Pass amps were not suited to this steady 4 Ohm load. Rumour has it that the 3.5's were designed around the then top of the line Threshold gear (earlier Nelson Pass designs). You may be on the right track but proceed with caution.
As a current owner of Thiel 3.5s; I would agree with Unsound's remarks. The 3.5s DO sound better when they have a higher powered amp to drive them. A Bryston 4BST would be an excellent choice. I'm a McIntosh fan - so I'm driving mine with an MC150 amp right now - though I'm considering a
possible move up to a Mac 200 watt amp later this year.
I would think the 5 would be up to the task as I had a 4B ST & replaced it with a 5. I had more efficient speakers than you do but on a comparative level the 5 did everything the 4B ST did in terms of adequate volume but much more musical. I sold the 4B ST as it was too analytical for me & subsequently sold the 5 as it wasn't quite what I was looking for. I now have an Ayre V-3 which I'm really happy with but will probably move up to a V-1.

I would say if classical, jazz & female vocals make up the bulk of your listening, then the 5 will do it for you. If you prefer rock, electronica, metal & so on it may not float your boat. That was my experience with the two amps.

Of course, the best thing would be to try an in home audition but even if you purchased & it didn't work out, you'd be able to resell easily. Good luck!
The Pass Aleph series are all single ended. That topology cannot operate in anything other than class A (and still be listenable!).
Get a used Plinius SA-100 and end your search ($1800 to $2100 depending on the condition). The Aleph 5,Bryston 3B, or 4B-ST will not have enough current to drive the Thiel CS 3.5.
With all due respect to Audiomax while the Pinius SA-100 might be a good choice with the Thiel CS 3.5's I don't think that the two Bryston amps lack the current any more so than the Plinius might. All would be at the very least adequate. In fact the Bryston 3B is probably very very close to the Plinius in this regard. I'm not so sure about the Aleph 5, but my guess would be that it too can handle the load.
I currently own Theil 2.3's and a Pass Labs x-250(synergy):) I have listened to most of the Thiel line up past and present. Before upgrading to the x-250 I was using x-150 again synergy. When auditioning the 2.3's I compared the aleph 2's vs the x-150. I personally preferred the x-150's. The x-150's goto 15 watts in class A mode. The x-250's goto 40 watts in Class A mode. The smaller amps I compared them to were absolutely terrible; not enough power. Now my Thiel's sing:0 Also owned the x-2 preamp and it is 90% of the x-1 which I know own.
At low level volumes I think it would, but i would opt for a higher power amp. Classe are know to be good matches with the Thiels like the CA 201.
FWIW and years later. . .

I have an Aleph 5 which I purchased to drive some now "set-aside" speakers. I purchased for the third time a pair of Wilson Watt/Puppy 5 speakers (can't seem to find anything I like better long term).

While the W/P 5 are not quite as inefficient as the Thiel speakers in general, the WP's are still a demanding load (ignore their efficiency rating of 94db) as they make wide swings from about 1.5 ohms and up.

The Aleph 5 (stereo amp, 60 WPC) sounds very nice with these speakers for my listening habits, room and volume levels. However, I was recently auditioning a Gamut preamp in my system and found that when I turned the volume up well past my normal "loud" listening levels, the soundfield congested.

I suspect this was mostly caused by a combination of my room and the available power from the Aleph 5 amp (I think it just ran out of juice). Now this being said, this was a listening level well beyond what I would ever sit and listen to for any length of time.

The Aleph 5 is rated at 60 watts class A. I don't know what it really puts out. Nelson is pretty conservative with his ratings. I also don't recall what this amp does in 4 vs. 8 ohm conditions.