I haven't listened to the AR SP-3 so no comment there but if by the the original HRT you mean the HRT music streamer that is not asynchronous then yes you can do a lot better. I own one and now own a nuprime DAC10. The difference just in dac quality is substantial. Even if you don't get the nuprime the HRT could be improved upon with some newer and very affordable Dac's. The nuprime is an excellent line pre as well. As good as your AR? No idea.
Is Spotify premium 16/44 cd quality? If not then you might want to try tidal Hi-Fi to see if you notice a difference.
Is Spotify premium 16/44 cd quality? If not then you might want to try tidal Hi-Fi to see if you notice a difference.