I have the same amp as you and a CD6005, i recently bought a CA Dacmagic Plus (wrote a mini review on here recently-ish). For me the new DAC offered a noticable improvement in the amount of detail i could hear, i would say that was its primary improvement sound wise - but what it did also offer me was increased usability (i can now plug my TV through my amp via the DAC, also listen to any kind of digi input like lap tops etc, also a number of input ports........although i had a bind trying to get my samsung phone to work).
Not sure if you get the functionality of a DAC separate from the SA8005, cant comment about SQ of SA8005 compared to the DAC Magic Plus as havent dont a direct comparison..........also the DAC magic plus is slightly out of your price range too, but i think you want the Plus version as it has twin wolfson chips and upsamples, the std version doesnt.
GL