Pass X vs XA amps sound quality in class A range

If you are one of those lucky enough and has the means to upgrade from the X (or X.5) to the XA (or XA.5) Pass labs amps, is there enough of SQ differences in low power ranges, say between 5-25W, where they all perform in class A mode, supposedly. Thanks for any insight!
I have owned both the X250.5 and the XA30.5. They both sound excellent. The X250.5 has great dynamic contrasts and bass control. IMO, the XA30.5 is slightly more resolving and relaxed sounding. In my system, I prefer the XA30.5. But I don't require a lot of power, either.

What are the speakers? How big is the room? How loud do you listen? Knowing the answers to these questions would help yield more valid advice.

I have owned the X250 and currently own the XA60.5's monos and agree the XA.5's are great sounding amps.
Thanks for your replies, I have the X250 driving a pair of B&W N802, room size is 32ft by 42ft by 20ft height, at their widest, a fairly large room and open to one side to dining room. Driving the speakers w/o the current meter moving (in class A?), it sounds mighty fine but when driven harder, there is a gradual hardening of the sound and loss of air. I am curious as my upgrade path should lead to either the X600.5 or the XA160.5. If they both sound similarly excellent at 50W/ch in class A, I would go with the X600.5 just to safe for those parties that I tend to crank it up.
The X don't sound as good as XA.5s given that the XA.5 provides sufficient power, they are not both "similarly excellent". So, if 160 watts is enough power for your speakers, room, and loudness levels you listen at, I don't think there is much doubt as to which of your two options is preferable.
I think Pubul57 is right. I suspect that the X600.5 and the XA160.5 are unlikely to sound the same, even at lower volumes. My understanding is that the circuitry designs of the two amps have significant differences, and that those differences are audible, even when both amps are operating in Class A. Certainly I can say that my X250.5 and XA30.5 didn't sound exactly the same, even when both amps were operating in Class A.

Your room is quite large, and you mentioned a tendency to listen at loud levels. So it is not a clear cut decision, IMO. It would ideal if you could audition the XA160.5's in your system, to see if they have enough power for your loud listening sessions. If it were me, and I could not audition the amps, I would take a chance on the XA160.5's. I have heard the XA100.5's, and to me, they sounded absolutely glorious. FWIW.

Hopefully other Pass owners with more experience than I have will offer their advice.

Much thanks again for all comments, I think you have answered my questions, that they sound different even at low power levels.
I owned the XA160 and switched to the XA100.5 and now the XA160.5. I have a difficult speaker load in a small room and don't usually listen beyond peaks of about 95dB with mostly classical music. There is no comparison between the XA and the XA.5. The latter is much better at all volume levels particularly in the handling of and control over lower frequencies. Sense of ease/flow, dynamics and air/space are also better. The XA.5 current delivery and doubling of power as impedance halves are big improvements over the XA model.

These are glorious amps in my system, but they are quite expensive. You should try to arrange a demo in your very large room to see how they sound with your speakers in your system to be sure before you buy.

You could also try asking Kent at Pass Labs or contacting Mark at Reno HIFI if you don't have a local Pass dealer. I have found both gentlemen to be very helpful answering questions.

You can read a more detailed review of my impressions of Pass Class A amps on my Audiogon review of the XA100.5. I am admittedly quite biased as I have owned many of these amps.
Thanks Pete, you may have saved me some troubles to just go straight to XA.5 class! Although my room is huge, my listening habit is low to mid in volume, to protect my hearing. In fact, with the lowly X250, I rarely see the bias needle move at all ever. But when I throw a party, it's different!
Keep in mind that when you throw your parties you won't be critically listening so these amps will play way over their class A ratings with no risk of clipping as they convert to class AB. You wiill probably be safe with a lower powered one.
I love my XA 100.5's. Replaced a long in the tooth Mark Levinson 27.5. They also warm up quick, say within 1/2 hour for good sound. I push Wilson W/P 8's with them. never once have they left class A bias. Great sounding SS power amps.
I have a small room (15'X16'X7.3') and don't listen very loudly. However, my speakers are 86dB with a 4ohm load and I just played the Chesky Drum Track LP at 95dB and my needles were moving all over the place, not pegged, but they moved about 3/4" every time the kick drum was struck. So that is with 320 Class A watts into 4 ohms, probably more peak power in Class A and then there is Class AB. I agree you probably won't clip them. I don't know the specs of your speakers, but you do have a very large room. With these Class A amps, I have found that one should buy the largest amp he can afford.

Is there any chance you can audition them before you buy?
However, my speakers are 86dB with a 4ohm load and I just played the Chesky Drum Track LP at 95dB and my needles were moving all over the place, not pegged, but they moved about 3/4" every time the kick drum was struck.

My speaker sensitivity is 92dB, so the 100.5's play way loud enough and the bias meters barely budge from their starting position.
had the same "problem" as peterayer, which i covered in my review in positive feedback. best solution: buy the biggest XA you can afford...and maybe you cannot. they're fabulous amps. (id own them if the heat of the larger amps weren't prohibitive in my small room in texas)
Another question for you all then: When the XA series exceed their rated outputs, do they cross over into class AB or clippings occur right away?
In the case of the 30 watts XA.5, clipping occurs at 130 watts into 8 ohms, higher into 4ohms. If you search the Stereophile archives, you'll find a review with performance measurements.
According to Stereophile measurements...

While the XA30.5 may give 30Wpc into 8 ohms in class-A (14.8dBW)...the amplifier doesn't actually clip (defined as the THD reaching 1%) until a much higher power level: 130Wpc into 8 ohms (21.14dBW). Even higher powers were available into lower impedances before clipping: 195Wpc into 4 ohms with both channels driven (19.9dBW), and 332W into 2 ohms with one channel driven (19.2dBW).

I assume the other amps in the XA.5 series will be similar in this respect, but I don't know that for sure.

I just read your review of the XA60.5 in PF. Well written and informative review. Thanks for the reference.

They switch into Class AB, not specified in the manuals and then clip at power ratings much higher. The XA.5 series amps are very conservatively rated. They do sound much more powerful than their rated specs would suggest, though I don't know the specifics. Kent at Pass Labs may be able to answer this question.
Thanks again, you folks are first class!
IMHO, if you think you might be pushing it from time to time for parties, etc., I wonder if buying the more powerful Class AB amp might be better. There's probably less chance of frying a tweeter with the more powerful amp, especially if guests get carried away.