Printing 32bit signed 2s complement data via JTAG UART

Yes, the audio codec returns a 16bit signed 2s complement sample which I am sending to the Nios system to be printed over JTAG UART (after squaring it).

Input signal: 2.4 Vpp, 500Hz, sine wave

Using volatile char *:

audR: 1 	 audL: -126	 audL2: 4
audR: 2 	 audL: 94	 audL2: -124
audR: 1 	 audL: 110	 audL2: 68	
audR: 1 	 audL: 11	 audL2: 121
audR: -3 	 audL: 8	 audL2: 64
audR: 2 	 audL: 7	 audL2: 49
audR: -1 	 audL: -3	 audL2: 9
audR: 0 	 audL: 12	 audL2: -112

Using volatile short * (obviously wrong results for audL2 since it is 32 bits but even audL is very different from char results):

audR: 0 	 audL: 12949	 audL2: -30023
audR: 1 	 audL: 956	 audL2: -3568
audR: 1 	 audL: -12180	 audL2: -21104
audR: -3 	 audL: 5486	 audL2: 15172
audR: 0 	 audL: 11626	 audL2: 28644
audR: 2 	 audL: -6731	 audL2: 20985

Using

#define USB_Ctrl (volatile char *) 0x00005000 
# define Data_in_1 (volatile alt_16 *) 0x00005010 // right channel samples
# define Data_in_2 (volatile alt_16 *) 0x00005020 // left channel samples
# define Data_in_3 (volatile alt_32 *) 0x00005030 // left channel samples squared
# define Data_in_4 (volatile alt_32 *) 0x00005040 // filter results
audR: -2 	 audL: 165	 audL2: 27225		 filt: 26076439
audR: -1 	 audL: 10419	 audL2: 108555561	 filt: 146741412
audR: -2 	 audL: -1139	 audL2: 1297321		 filt: 16184391
audR: -2 	 audL: 1243	 audL2: 1545049		 filt: 36079690

Removes the negative results problem, but I don't know how to make sense of this sample data now. how do i properly convert these sample values to a real voltage? Since I'm using 16bits, the ADC has a resolution of -32768 to +32767. The step size would be Q = (3.6 - 1.8 V)/2^16 = 0.0000275 V = 0.0275 mV (I'm a little unsure of the input voltage range for WM8731, the datasheet says the analog supply range is 1.8-3.6V). Is this correct?