beans-on-toast

I play for myself. The sound guy works for the audience. Hopefully they are both as good as they can be.

I too like getting in front of an SVT and a wall of sound. How you monitor and interact with the amp and speaker cab is important in terms of your playing. Very true about not all sound engineers being equal.

There is no right or wrong. You want the best sound you can get factoring in the cost/time to achieve it. Many argue that the audience wouldn't appreciate the difference. As a player, I want whatever is going to inspire me to play the best. Live recordings from the 50's/60''s/70's that I like are all mic'ed amps, recorded with analogue tape. That's my highest benchmark. I do use DI's when called for.

It's a complicated question. The DI out from an amp is normally pre-amp out, that can be post or pre-EQ. An external DI might be post power amp where the DI is connected parallel to the speaker cabinet. The advantage of this is that there's a contribution from the power amp. Of course, a DI doesn't need to be through an amp at all. Mic'ing a cabinet can be accomplished in different ways. The sound of the cab contributes to the tone. The speaker can be close mic'ed. The position of the speaker matters. This can make the sound brighter or more bassy. The mic is important. It makes contribution as well., every mic has a characteristic frequency response. The cab can also be mic'ed from a distance, for instance a meter away. This allows the mic to pick up room ambience. I like the sound of some air between the speaker and the cabinet. Tone can be contoured by the mixing desk. Digital desks allow for all types of plugins to be used. This includes high pass/low pass filters, compressors of all types, speaker emulations, effects, etc. In this case, the sound person will usually want a basic signal. All this allows for a lot of different options and ways to approach the tasks.

If one cab is more efficient than the other, it may sound louder. This is true even if the speakers in each cab are the same. The cabinet designs factor in to how well they play together. You'll never know till you try them together. When using different cabs together, it never hurts to first perform a battery test on each one separately to ensure that they operate in phase with one another.