I have been playing guitar since April. I have a brother in law who has been playing for 40 years that I consult with. Several times he has asked me to send recorded sampler I have played of a piece we are discussing. My rig is purely digital. I use a Line 6 Floor POD Plus that I listen to through head phones connected directly to the Floor POD or via a PC speakers connected directly to the Floor POD. I want to use Audacity to record what I am playing using my PC and the Floor POD.
It seems I am having configuration issues with Audacity. What I have done successfully is plugged the head phones “out” to my Mic or line in on the PC sound card. When I do this I get the full robust sound I’d expect when listened to via the speakers connected to the PC or via head phones plugged into the PC. When I record with Audacity connected this way Audacity records at seriously diminished levels. I have checked all of the PC hardware and Audacity configurations. I have run the whole spectrum of settings and boosters and still cannot get the Audacity recordings to record with full levels and robustness.
What would be causing this issue? The way I am connected to the PC works fine for the PC, why not Audacity?
What I have done successfully is plugged the head phones “out” to my Mic or line in on the PC sound card. When I do this I get the full robust sound I’d expect when listened to via the speakers connected to the PC or via head phones plugged into the PC.
I’m not sure what’s wrong… If you are connected to line-in and you’ve selected line-in as your recording source for Audacity, you should be recording exactly what you are listening to on the PC speakers.
What kind of levels are you getting? When you look at the waveform in Audacity, how big are the wave peaks on the 0 to +/-1 scale? If you are getting up to around 0.5, that’s OK. You can use the Amplify effect to bring your levels up to 0dB (0dB is "100% or 1.0).
In general, homemade recordings don’t sound as “loud” as commercial recordings, because there is lots of dynamic compression used in (most) music production.
…If you have a laptop, make sure you are not recording with it’s built-in microphone. 
And if you are using a laptop, since laptops usually don’t have line-in, you may need an additional USB audio interface in-between the POD and your computer. You’ll get plenty of volume from line-in, but usually poor quaity.
And, you should be using line-out of the POD to line-in on your soundcard. (You may need some different adapter cables.) Headphone-out is an acceptable match for line-in, although you might need to adjust the volume louder than you’d have it for headphone listening.
The mic input on a regular soundcard has too much gain for a line/headphone signal, and is just worthless for quality recording. (It only works with “computer mics” and is the wrong interface for any good stage or studio mic.)