Way I see it, you've got $1,000 invested in the preamp and another $1,400 for the amp, and $2K on the Salk ST's (all prices new / retail), but essentially less than $400 in the DAC, if we consider the Nova Pre's internal DAC to be broadly similar to the Peachtree Dac IT, which costs $400 retail. I wouldn't be surprised if it's the same board (same DAC chip for sure). But not having the external case, power supply, etc, means actually it's less than $400. And by now it's at least a 2 year old DAC, which may not sound like a lot, but in DAC unit years, it's middle-aged entry level DAC.
Not to suggest that every component in your system should or needs to cost broadly the same amount of money, but I think it's safe to say you're underinvested in the DAC in relationship to your other components. As for the Auralic Aries, I agree it seems great for functionality and sound quality, and am actually planning to get one. But inn terms of return on investment in your situation, a beter DAC vs the streamer / transport is going to make the greater difference. The Oppo 103 is more than up to the task of streamer for now.
I agree with what someone previously said about diminishing returns in audio, but at the $2k or so budget you've set yourself, you can definitely move up to a substantially better sounding DAC than you have now, something you can start enjoying now and that may carry you over to a future system. I wouldn't spend much more than $2k on a DAC though, unless you're deep pocketed, as the technology / improvements is still moving too quickly to safely make much more of an investment.
