Okay, I see what's happening.
The Sennheiser e906 is a dynamic mic with a low sensitivity. The sensitivity of that mic according to Sennheiser's info sheet is listed as being 2.2 mV/Pa. This translates into a sensitivity or -53 dB ref 1V/Pa.
In regular English it means that mic needs a lot of volume into it - or a mic pre that will give you something in the 50 dB gain range - to output a strong signal. For comparison most condenser mics have a sensitivity in the -30 dB range. The e906 at -53 dB will give an output to the Apollo that is 23 dB quieter than a condenser mic.
THe e906 is made for recording loud guitars. Turn your amp's volume way up.
All mic pres will give unwanted noise when run in the upper part of their gain setting. If you have the Apollo's gain set above 45, it will start to give you more noise. This is why some high-end mic pres have as much as 80 dB of gain, so they can be run at 50 dB without adding noise.
So crank up the guitar amp and have at it. If that is too annoying to others in the house, then a mic booster like a Cloudlifter or FEThead will solve the gain problem, or use a mic with a higher sensitivity.
I think the buzz sounds you are hearing may be either from the mic cable placed over the amp being too close to the amp's power supply transformer, or your guitar is picking up the 60 Hz buzz from the mains (assuming you are in The States), otherwise 50 Hz.
HTH
:- Don