Definitely a 103 + $800 dac. Plenty of other people do SS mods to the oppo 105 - one I heard from ex CJ guy Bill Thalmann at Music Technology smoked the Modwright one - but costs $1800. First thing he did was remove the big multichannel analog board that constitutes one of the biggest differences between the 103 and 105. Then put a better clock in it, then a discrete analog output stage, then improve the power supply, etc.
I'd definitely not use the internal volume control either for critical listening, especially for low level listening, unless you enjoy digital truncation.
The 105 does a lot of things well in one box for a decent price. But I'd put the internal dac part at $500 equivalent and mostly because of the linear power supply.
I have a different take. I think the DAC in the Oppo is as good or better than most any of the 800.00 DAC's out there. As stated earlier, the fact that Modwright did not even bother to offer a SS upgrade for the 105 is a testament to just how good the analog output stage actually is. BTW, more often than not, the largest sonic deltas between DAC's IS the analog stage.
Regarding the volume control, if you have it set at low to mid volume, that is one thing. However, if you just adjust the volume between 85 and 100, it's not really noticeable in terms of audio quality.
I've been through a LOT of DAC's, and trust me, there is a lot of hype associated with them, compared to actual audio performance deltas. So' take all our "opinions" with a gran of salt. If possible, try to audition the units before you purchase.