Well after all the fiddling I had two dissapointments, firstly on Play / Pause or track change there is an almighty 'crack' and when muted there is a background ticking noise.
I had read on the Adafruit website that to avoid the 'popping' when playback starts or stops then a) it's down to a Raspbian Linux thing, b) sorted by outputing a fixed sample rate to the I2S device so the bit clock does not change.
I tried messing around with the 'Audio Resampling' settings but this made no difference and I had seen on the Volumio website other people having the same problem with various DACs so as I had a generic I2S 5102A DAC knocking aroud (cheap and cheerful from China) :
I thought lets hook this up with some powered speakers and have a play (connections are as below):
VCC --> Not Connected
3.3V --> 3.3V
GND --> GND
FLT --> GND
DMP --> GND
SCL --> GND
BCK --> PIN 12 ( GPIO 18 )
DIN --> PIN 40 ( GPIO 21 )
LCK --> PIN 35 ( GPIO 19 )
FMT --> GND
XMT --> 3.3V
OK so that worked, but still noise etc. Now I have tin ears and my MP3 collection has file encoding of masssively varying quality so I set the DAC type to 'Generic I2S DAC' and then set the 'Audio Resampling' as below:
The result, no pops when starting play from paused, no pops when changing tracks, no ticking noise when muted.
I didn't really want to have to either keep recharging or supplying power to the speakers, so time for an amplifier. Remember the original idea, I wanted a small player that had it's own amplifier and speakers that could sit on the desk / shelf next to me whilst I work.
Enter the PAM8403 Amplifier board.
It's a Class D, 3W per channel amp (into 4 ohm speakers, it drops to 1.8W with 8 ohm speakers) that runs from 5V. Oh yes and it cost 40p, a quick hook up later with some old speakers from a defunct HiFi unit, fire up Volumio and...it's too loud even with the volume level down at 1.
Not wanting to end up over driving the amp I had a fiddle round with some resistor values and ended up using a 6k8 and 3k2 divider as so:
That give a just audible output at a volume setting of one.
So next thing to do is draw up the connections and post it up here, then build a case.