Here's the deal with these bargain basement DVD players, that offer otherwise very good DAC's and processing for standard pcm, and better for DVDA and SACD playback: Basically, you get what and have suggested for audio playback - a bit limited dynamics, constricted sound, not so musical, sweet, and full bodied sounding, and maybe lacking some extension and air. Overall, the sound is not as refined as what's out there, if you're after the ultimate sonic experience from your investment.
On a more "goal oriented" note, I've found that passive speaker systems in general offer somewhat limited dynamic expression and tranparancy, to offer a sense of "true realism", if lacking speed, impact and dynamic contrast overall. Using equipment that's dynamically challenged, simply moves one away from "the goal", if the highest sonics possible is what one is trying to attain from their system. (building a high performance system is like tweaking a race car. Better parts, more knowledge, and a heck of a lot of tweaking and patience will ultimately yeild you a better race car)
Back on task. Overall, however, compared to the digital processing from 10+ years ago, these bargain DVD units are simply supberb!...specially SACD and DVDA playback from these units.
I myself had been using an old Panasonic DVDA-310 from 10 years ago, which was a world beater for a DVD/CD player, retailing at $699 when they came out - reviewed as "better than Levinson Separates, at at that time by Absolute Sound (May '98 issue). I have been very happy with it for CD and DVD music for years. Simply superb! And yet this player, like the Oppo's being mentioned here, still aren't perfect units by any means.
The better quality transports and DAC combo's also offer what and are hinting at, specifically much more accurate dynamics and dynamic contrast, overall weight and speed to the sound, better air and delicacy, more body and richness to the sound, soundstaging, etc!
That's not to say the budget players with the advanced digital processing are not good, they are simply outclassed on a purist level, if you have the money to invest in "the best!".
For budget conscious, yes, you will do very well with what these units are offering - however a good digital connecition from some from some of the better transports and DVD units out there likely can do as good or better of a job connected digitally to an outboard pre/pro or processor for digital playback!(processing in the outboard receiver, pre or processor). As standalone units, they can, yes, be mod'ed, for even better results. But then that gets you closer to the more expensive units out there. And, I suspect something like a used SACD player from Sony would still beat it in all areas of audio playback for the same money. So consider (all those looking for sonoic nirvana for $100 or so)
Basically, you get a whole lot for a little -relatively speaking - from these affordable digital units these days. You simply get more when you spend "significantly more" with better transports and standalone processors, IMO.
But, shopping on the net for used can save you even more, and give you more options.
I guess, like those above, it's probably more truthful to inform those seaking the highest end sound they can budget, that spending $160 on a DVD player won't "get you all the way there". That said, shopping for better quality "separates" is still not easily thrown aside from some miracle budget piece made in some country where there might not be any running water...so consider.
Would I still buy an Oppo myself? Sure! I'd probably have it moded, even use it just for DVD playback and upscaling (and thus DD/DTS digital out). But I'd still likely end up with better CD separates, SACD players and other, if I was really into higher end sound - and I am.
"IT'S ALL GOOD! Some's just better than others..."