What effects soundstage more ....

(Long) Judging from your post, it seems that there's more than one question: soundstage, tonality, low frequency reproduction...
You also mention two reputable amps -- so one obvious thing to do is switch pre-amps and listen for results. Or you could try a bigger Plinius... However, read the following if you can spare time.

Soundstaging is a systemic thing and is influenced by a number of variables (in no order):
*the original (i.e. the recording)
*the room and speaker placement within it (i.e. reflections can spoil precise imaging)
*mid-range & hi-frequency reproduction, from source &/or speakers &/or pre &/or amp -- even wires can introduce phase anomalies
*phase

OTOH, the perceived BASS reproduction is usually a matter of driving capability from the amp -- assuming there IS low-level signal and that signal reaches the amp and your speakers are capable of going low. Since you heard it with one combo, we'll assume that signal is there (you didn't hear "one-note" bass -- i.e. boominess??)

The tonality you refer to is usually a matter of "voicing" of the component(s) used. Your description of the Plinius sound tallies with many others', so no surprise there.

Your description of the Pass sound ("harshness"), however, may mean that there is a slight emphasis in the mid-range at around 3kHz & up, that's especially annoying to our ears.

Looking them up, I find the Obbligato have mid-range units covering a range from ~100Hz up to ~8kHz where a supertweet takes over. This sort of design tallies with your impression of "revealing" speakers -- i.e. there's no xover in the critical mid-range where our ears are VERY sensitive.

So, obviously the Pass combo excites these drivers more in that range than the Plinius.

Ultimately, and if you like the speakers, I would suggest you try the two amps in PASSIVE mode -- just to determine if differences are amp related. You'll need a volume pot value that can drive the amps (say 4x or more the input impedance of the amp). Good luck!

You could give Ernie at the Inner Ear Mag an e-mail. They reviewed the obbligato's some time ago. He could tell you what amps they tried them with. I do remember they loved this speaker. Good-luck...

What cabling (IC and S/C) were you using? I've found that to make quite a difference.

You might try a larger Pass amp. Soundtage tends to collapse and the sound becomes etched and strained as the amp runs out of gas.

Cpdunn99 I agree with you, cabling does make a differrence,
I both tried the Pass X250 and the Plinius, I own the
Plinius SA100 for 7 years now, This 2 amps, both have
Big soundstage,with the right cabling.The X250 likes
the Harmonic Tech, The Plinius likes the Tara lab master
gen,I auditioned them both with Art audio preamp,and
Adcom GFP 750.Interconnect I used the Silway and truthlink.
Good Luck.

As far as "harshness" goes with the X2.5 / X-250, look to the source, preamp or cabling, not the amp. As far as cabling goes, Pass X series amps and Goertz MI-2 speaker cables were made for each other as far as i'm concerned. If you want lush sound that is truly clean, coherent and airy with a phenomenally deep and wide sound stage, this is a hard combo to beat. This is especially true if running lower impedance speakers, which the X series seems to work their best with. Can't comment on the Plinius as i have very limited experience with their gear. What gear i was exposed to of theirs wasn't very favourable at the time. It was a completely unfamiliar system though, so that experience doesn't count for much to me. Sean
>

PS... If you're not running your X-250 off of a dedicated 20 amp line, don't expect it to perform like it should. It should also be left on 24/7. Listen to it after three days of continuous power and you'll think that you're hanging out with angels in heaven : )

The Pass gear should not sound harsh when set up properly. I agree with Sean (as i usually do) that you may want to look at your cabling and be sure you are feeding the X250 adequate power. Power cabling also can drastically change the sound of the Pass preamps. Power cables don't have as great an effect on the Amps as much as the preamps.

I use dedicated lines, but I never have had the harshness you report with the non-dedicated lines. Non dedicated lines' quality is also dictated by what else is on the line. I had nothing using the circuits, but they were open and had cabling run to unused outlets via smaller gauge than is used now on my 10ga dedicated lines.

I use Synergistic cables with the Pass gear I own and have never had anyone express any notice of fatigue or harshness with any of my sources.

Ultimately, you should mix and match components to see if you find a mix that suits your tastes. I am fairly certain that the X250 isn't running out gas unless it is receiving an inadequate voltage from the wall. Try a different set of cabling to determine if that is the incompatibility issue causing you to be discontent. Best Regards,

Plinius is "voiced" with Siltech wire. I prefer copper, myself, but that's just me.

I think I am going to try to change out the preamps and see what that does to the sound. All I want is the tone of the plinius set with the soundstage and low frequency weight at low volumes of the pass set. I do not have a lot of experience with cabling ( the ones used in this audition were Harmonic Technology IC and XLO s/c ) but what would be easier to accomplish with cabling, a bigger soundstage and low frequency boost ( this could be gainied with better placing of the speakers maybe? ) or sweetening the tone throughout all frequencies? Or is that too much to ask of cables?

I am leaning towards getting the pass setup. I do not plan on my current speakers being the ones at the final step of this process. I imagine some time down the road upgrading those so I think the pass stuff allows me more flexibility on speakers ( in the case of a power hungry speaker ).

I appreciate all of your comments. Thank you for your time. Also anyone else feel free to chime in on your thoughts/experiences.

While this is years later, my experience confirms the OP that the harshness in the Pass 2.5/250 is pretty normal. The 250 can be a bit harsch, as Nelson Pass will completely attest to and hence the move to the 250.5 which was much smoother and subsequently again to his new amps, which are even more smooth. This being 2010, there have been a lot of improvements with Nelson's amps, towards less strident or smoother performance. I does not surprise me that the OP encountered this scenario with the Pass and at the same time felt the plinius' soundstage did not hold up to the pass combo.