It is perhaps a little difficult to answer the question. In the real world, one obviously can hear a amp + cab without a microphone (just by standing near enough with functioning ears), but obviously all
recorded sounds -- and this effectively includes cabinet impulse responses, whether those of the cab room built in to AmpliTube or a 3rd-party IR -- require a microphone.
Moreover, guitar amplifiers are intended to work through guitar cabinet speakers, which sort of serve as a kind of EQ. The raw sound from all amplifiers generally sounds horrible if you send it to relatively flat (in the EQ sense) speakers.
Obviously, you can bypass Amplitube's cab room entirely and send the signal to your computer's headphones or speakers (which will almost certainly by much flatter than any guitar cabinet's EQ response), enabling you to hear that horrible sound.
However, this is not likely to get you anything that you want.
Any speaker (even without a microphone) is going to shape the sound of the signal from the amp. A speaker with a relatively flat response will shape it less, while a speaker with more pronounced EQ curves (as typical in guitar/bass cabinet speakers) will shape it more. So, although you can bypass AmpliTube's cab room and send the raw amp signal directly to your own speakers (of whatever kind, including headphone speakers), obviously the result will sound at least slightly different in different speakers.
And, then, any recorded guitar sound you've ever heard has gone through guitar cabinets (real or simulated!) as well as microphones (real or simulated) and quite probably a variety of other post-processing (potentially including mic preamps, analogue consoles, and other gear, tape machines, and tape itself, etc.). Even live guitar that you've heard in concert has (almost certainly) gone through cabs/speakers (real or simulated!), mics (real or simulated!), and in all likelihood a bunch of PA equipment (as quite likely other processing).
Bass may well be recorded (or sent to the PA) as DI ("direct injection"), and you can also do this with guitar, of course, though this entirely bypasses traditional "amps" anyone (and the sound is still generally processed in various other ways).
Ultimately, "the 'true' sound of an amp" is a bit of an illusion -- or at least a chimera. You will seldom hear anyone's raw amp sound because it is so nasty
and is
expected to be processed through
at least cabs/speakers, while microphones are just an unavoidable part of the recording process or the use of digital IRs since you can't record real, physical soundwaves (or capture impulse responses) without them.
Effectively, speakers, cabs, mics, etc. are all just EQ curves applied to the raw amp signal to make it less nasty.
You could, of course, synthesize any such EQ curve into an IR that you wanted, but you are inevitably processing that raw amp signal in some way. cabs, speakers, mics, etc. -- and their digital simulations -- are all just ways of adjusting the final EQ curve in different stages.