Which is Better? Modded Denon 5900 or Teac DV-50

First, the DV-5o exceeds the 5900 in all aspects of performance. The 5900 does not upsample, or have the D/A convertor build of the DV-50. The 5900 is a good machine but only exceeds the DV-50 in price not value.
Second, A digital out would permit you to make digital copies.
Third, Sacd and DVD-Audio will both fade away as the Blu-Ray technologies come to fruition.

I have a fully two modded Denon 5900 by Underwood including the superclock and power supply mod as well. I also have a Rick Kern modified Teac DV-50 (a $300 mod vs about $1700 for the Denon). The DV-50 blows the doors off the Denon which I now use in my second system and works well with rock music but
I find too forward with classical. Hope this helps.

The Exemplar/Denon 2900 clearly outperforms the Teac DV-50 and stores that sell both can no longer sell the Teacs. I do not know anything about the Underwood mods, but the Dan Wright mods on the Sony pale in comparison with the Exemplar.

There are dsd output transports but all must be used with their dacs.

All rotating media will soon be replace with USB plug in media.

Fgm4275 / Theo- There are already several transport / players on the market that provide a digital output for DVD-A and SACD. The new Sony SCD-XA9000ES (SACD only), the later Pioneer universal players, etc.. The digital outputs, in all cases, are encrypted so copying is not possible. In some cases (eventually all) you do not need Sony to Sony, Pioneer to Pioneer, etc.. Recently, one of the British maganzines played a SACD via a Pioneer player into the Sony TA-DA9000ES multichannel receiver via the digital link with no problems (even had a picture of the Sony's display clearly identifying the link-up). We're getting there!!!