Oh, I understood most of that. So, it's possible to be subsonic and be traveling faster than sound(relative..). Got it. If the airplane were making noise loud enough to be heard from the ground, those sound waves would all be behind the airplane(relative to the ground). It seems like it would concentrate a lot of sound into a bow wave. I thought this may resemble a boom, but apparently it's not even close. I was confusing sonic booms with sound waves, they are totally different.
I think the point that you are confusing has to do with what the sound coming from the plane does after it leaves the plane. Let's hit that for a little bit:
Ok, we've already covered the fact that a sonic boom is really a shock wave caused from the fact that the airplane is traveling faster than the speed of sound relative to the air. Why does this even happen? (... it will be a little bit illuminating when we talk about sound waves later...) Well, when an airplane (or anything else for that matter) is moving through the air at sub-sonic speeds the air has to move out of the way of the plane as the plane flows through the air. The air molecules and the "plane" molecules can't occupy the same space at the same time, right?
So, here comes the plane, and the air molecules nearest to the surface of the plane hit the plane and bounce off. As they bounce back off the plane, they hit other air molecules in front of the plane that have yet to be disturbed by the on-coming plane. Those air molecules in turn hit OTHER air molecules even more in front of the plane, et cetera, et cetera. So, in sub-sonic speeds, air molecules way out in front of the plane are getting pushed out of the way of the plane well before the plane gets there (it's still tiny fractions of a second... but it's BEFORE the plane gets there, none the less).
That signal, or that wave if you prefer, that results from air molecules bumping into other air molecules is a sound wave. All sound is just a bunch of air molecules bumping into each other, and then in turn those molecules bumping into OTHER air molecules, and on and on. But there is a maximum speed at which that can happen... the speed of sound.
If a plane is going faster than the speed of sound, the signal "transmitted" from air molecule to air molecule to the air in front of the plane takes longer to get there than the plane ITSELF does. So the air in front of the plane doesn't have time to get out of the way, and instead of flowing around the plane the air molecules right next to the plane get smashed (or compressed) between the air in front of the plane and the surface of the plane... this is the shock wave, or as it is sometimes called, the compression wave, that causes the sonic boom you hear. At this wave, a whole host of the properties of the air are forced to change over a very small distance, including the temperature, pressure and density of the air as the air gets "squished." It's a violent process.
Now, what about when we are subsonic? First and foremost, subsonic and supersonic can ONLY mean relative to the surrounding air... which will become clearer in a few seconds. So, regardless of a headwind or tailwind, we are subsonic relative to the surrounding air. Our plane's surface pushes the air molecules right next to the plane out of the way, and this signal is transmitted as sound through the air. Those signals (SOUND) travel... at the speed of sound, of course. For lack of a better way to write this, once the sound is in the air, it doesn't care what happened to the plane that made the sound. It isn't like they are "tied" together, with the plane "dragging" the sound. They are not. So... they can't get "bunched up" or "concentrated" or anything. They move outward from the plane, through the air, and in every direction including forward. Even if a plane's true airspeed plus the wind equates to a speed higher than the local speed of sound on the ground, sound waves from the plane will reach the ground before the plane passes overhead.