Regarding filters, I've heard DACs with standard filters, either just a default/single option or with multiple options to choose from, and DACs with off-the-shelf or, better yet, custom filters. I'd like to say I prefer minimum phase over linear phase, but for most D/S designs, I generally found I just prefer less oversampling than more oversampling (i.e. 2x vs 8x, 2x being preferable to my ears). Slow roll-off vs sharp or fast roll-off. Etc. Then again, I most prefer a non-oversampled design, which I know for some is a quick way to disconnect them from the music. Just rolling with what resonates best with me.
On the other hand, I've heard 8x oversampling filters that were really quite pleasant. The Theta Gen Va has such a filter. No hint of glare, digital hash, or any other similar unpleasant characteristic. I've heard some standard 8x filters that weren't so bad either, usually from Wolfson-based designs.
Sure, most standard digital filters are probably nothing to write home about. I think some are better than others. For example, I like what Wolfson does, and I like DACs that utilize the variety of digital filter options available from Wolfson. Gamma2 and some of the Audio-GD DACs are good examples of this, with A-GD being awesome for having options ranging from 2x through 8x oversampling with various roll-off types. The PWD Mk1 I tried was a very poor example. All of the filters were 8x, and PS Audio ordered the filters differently on the DAC than what they specified in the manual, so I've never really trusted them to be competent after that despite some liking the PWD Mk2 (Mk1 -> 2 upgrade, that is). But, even then, 8x oversampling or not, I didn't care for the PWD Mk1's sound all that much. It robbed the Wolfson chip of what it did best compared to other D/S chips in terms of tone, liquidity, and so on.
Anyway, while I generally prefer less oversampling (or none) over more oversampling, clearly there are exceptions to this rule or certain options and implementation I don't mind using standard, off-the-shelf, or entirely custom digital filter designs. I don't think it's right to simplify it down to linear phase vs. minimum phase, more ringing vs. less ringing, pre-ringing vs. post-ringing, 0x through 8x oversampling, and so on. Way too many other variables to consider in the DAC.
But all this talk of digital filters, linearity and accuracy, resolution and detail extraction...none of this touches on where I think R2R/multi-bit really shines. I just have not heard a single D/S DAC that gives the three-dimensional, full-bodied sound, real sound that you get from R2R/multi-bit. And by full bodied, I don't mean warm or bassy, though R2R/multi-bit does usually seem to have better bass slam, texture, and pitch differentiation assuming good chips and a good implementation. I mean that each instrument, voice, and fart sounds like something that has some sort of real presence and body to it vs. some sort of flatter, 2D representation of said element. D/S generally just sounds like a cheap imitation, good detail or not, and I find it difficult to go back to D/S DACs now.
