Hello overg1 and welcome to the forums.
overg1 wrote:1) There are so many volume knobs to turn, which one of them should I use when I want to make the sound better?
- The voulme knob at the guitar?
- The one at the Audio interface?
- The one in the Amplitube software?
- The one in the amp simulator of the Bass Man 59?
- The headphones volume?
Well, depending on how you want it to sound, it's a combination (although 'better' sound is subjective). As long as you are gain staging correctly you will get differences within the software, however first things first:
After plugging your guitar into your AI, check that the level going in is appropriate. Personally, I start with the volume on the guitar at its highest. Then increase the gain on your AI input until the input level showing on its meters averages around -12dBFS. Try and keep loudest peaks to -6dBFS. This is the important bit of gain staging as once it's gone through your AI it becomes a digital signal, rather than analogue.
After that, it's all down to a matter of taste and what kind of sound you are hoping to achieve. The input level control on the (bottom left) of the AT4 GUI can then be raised if required, but has no bearing on any recorded signal if you're using AT4 in a DAW. The volume on the amp module replicates the real world volume control so can introduce breakup on the speaker if required.
The headphone (or monitor) level is purely an analogue control of your AI and the only rule there is to set it to a comfortable level, but be aware of possible hearing damage should you push it too far.
overg1 wrote:2) How can I add the missing modules?
You're probably seeing this message if you try to open a preset that includes gear that you do not own. You can add missing modules by buying them via the Custom Shop app that would have been installed along with AT4. You can also use the Custom Shop to trial any module before you buy it.
overg1 wrote:3) What amp is recommanded for Gibson 335?
Really this will be a personal choice, depending on things like the style of music you're playing, what sound you want to achieve, your playing style etc.
overg1 wrote:4) How can I add reverb? Is there one implmented in Amplitube for all amps? Or do I need to buy speical effect pedal?
You can buy stomp effects and rack effects to add reverb into your tone, as well as some amp models including it if it was on the original unit. If you are using AT4 within a DAW, you can add reverb there as well.
Hope that answers your questions.