This was a copy of a set-up of a SDR-4+ receiver on a Mac. It was pasted out another email so I've lost who sent it to me:
 
"Re: SDR-4+ and Mac OS X

SDR-4+ now up and running with DSP Radio V1.3.5(1)

Took a bit of head scratching, but got there in the end. This blog helped point
me in the right direction, but the settings are slightly different.

http://blog.marxy.org/2012/02/softrock-ensemble-rxtx-with-dsp-radio.html

When you plug the The SDR-4+ USB cables into the Mac, they show up as:

USB Audio Codec (0 in/2 out)
USB Audio Codec (2 in/0 out)

In the Mac Audio MIDI Setup, you heed to create a new Aggregate Device. Click
on the default name 'Aggregate Device' and rename it to something useful like
'SDR-4+'. From the list of devices that show in the new device, select (Use):

USB Audio Codec (2 in/ 0 out)
Built in output (0 in/2 out) - and tick the 'Drift Correction'

The clock Source should be USB Audio Codec and the sample rate 48000.0 Hz (Is
this correct?)

Run DSP Radio http://dl2sdr.homepage.t-online.de/

Show the DSP Radio Audio Devices window and scroll down to your new Aggregate
Device, if you renamed it, you won't have any trouble finding it! Tick the
Input and Output boxes.

Show the DSP Radio Configuration window and click the 'Add Configuration'
button. Click on the default New Configuration name and change it to SDR-4+

The Input I and Input Q are the feed channels from the SDR-4+ sound card. I've
set I to Input 0 and Q to 1 (not sure I've got these the right way around, more
testing required)

The Output I and Q are the Mac soundcard output channels. I've set I to 0 and Q
to 1 (not sure this makes any difference which way around they are?)

DSP radio doesn't have the easily available user options that Windows SDR
software has, but do play with the settings in the DSP Radio Configuration
window. I'm using the following settings:

AGC - On
Input Gain - 10
Output Gain - 10
S-Meter Gain - 1
Spectrum Gain - 0.3 (sets the waterfall contrast)
Epsilon and Alpha - 0 (no idea what these settings are!)

You can keep this Configuration window open whilst DSP Radio is running and play
with the settings to see the effect.

When you do run DSP Radio, don't forget to cycle up/down 10 Mhz or so to reset
the SDR-4+ filters otherwise you won't get anything.

Please bear in mind that some of my deductions are pure guesswork, so pleas e do
correct me if I've made any errors."

Regards,

Chris G4HYG