First Post here - Normally lurking in the Vinyl Circle - Hi

Looking for some advice.
I've downloaded a streaming app on my 3GS Iphone (Zumocast), which is successfully pulling down audio from my PC and is nice and simple to use.
Currently using a std. 3.5mm stereo to twin RCA lead to connect to my amp, but the sound (not unsurprisingly) is rather compressed when compared to playing CDR audio discs from the same source data.
Am suspecting this is down to the DAC and output circuitry of the Iphone.
I have a very nice DAC residing in a Pioneer CD recorder which I've connected previously to a PC digital output with great results.
So I'm trying to find the best way to get a digital output from the phone to this.
Have had a quick snoop around the web to see if there's any reasonably priced Gizmos or docks with a digital output.
There's plenty of rather large and bulky units with DAC's which I don't really need.
Ideally I'd like something a little smaller and discreet to sit relatively unnoticed alongside the rest of my gear as it will only be used occasionally.
Is there anything out there that fits the bill?
Any thoughts will be most appreciated.
Cheers
Dave