My board has a 5V and 3.3 V.
I directly connected the MOSI, MISO, and SCK of the SD card to the MOSI, MISO, and SCK of my arduino.
I also directly connected the VCC pin of my SD card to the 3.3V of the arduino.
After connecting everything, I checked the voltage at the 3.3V pin of my arduino.
I used a fluke to measure the voltage. I got a reading of 4.3 volts.
I'll try the 100uF. It might work.
Also, I'll try connecting the audio out to pin 9.
I believe you are referring to the outputs/pins....
but this does NOT mean your board runs on +3.3v logic level..
example the Arduino UNO has +5v & +3.3v output pins....
however the boards runs on +5v logic... (even though there is a regulator outputting +3.3v on a pin or two)
I have tested/used this library on custom boards, Uno/Duemilanove (+5v).. and even minimal Arduino circuits running on +3v, 8Mhz internal clock (ie: no crystal no caps..etc)
First thing is to get an SD shield that properly works with your set-up..