(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 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!