PS:
SICR, before I got the Focusrite 18i20 for my iPad, I (not really) used
http://line6.com/mobilein/features#studioquality
http://line6.com/mobilein/specs/
http://line6.com/support/manuals/mobilein/
When I played guitar by this 5cm*5cm*1.1cm thingy via the iPad 2
"speaker" the neighbour living above me listend through the ceiling and
liked my guitar playing.
I seriously doubt that any guitarist or concert audience would like
the sound. We could play nice tunes, rocking riffs etc. by even the
crappiest devices and we could play in an ungifted way using the most
pleasant guitar amplifiers as well. The more we a trained, the better we
could cover odd sound and even if we are unable to cover the odd sound,
a nice tune still remains a nice tune, if the sound is bad.
Beginners playing guitar easily could play fast heavy metal solos with
an overdose of overdrive, because unclean playing isn't much
noticeable. There is a similar effect when a good guitarist plays clean
jazz solos by a warm tube amp with a 12" speaker. It doesn't cover
unclean playing, but adds something pleasant to the sound.
Just something that fits the impedance not necessarily provides
an e.guitar sound we like. Len mentions that he at least use a speaker
and a mic, IIUC even when not using a guitar amp. Most important for a
pleasant guitar sound are a guitar pre-amp and a guitar speaker,
usually 12".
An optimized impedance doesn't grant anything, it's important what
follows. Even a good amp and speaker emulation can't be pleasant, if
the input circuit is crap, unsuitable for e.guitar pickups.
The OP noticed that when using a device that doesn't provide the
optimal impedance, it's still possible to get a pleasant guitar sound.
Yes, this is possible, sometimes we have good luck.
In my decades of experiences the impedance is not the only relevant
aspect. It's even not the most important aspect. It's a chain of things
that is important.