Tclipse: I had the "reference upgrade" done to my 850 by GNS back in late 2000. I'm still enjoying it. I now run it without a preamp. Compared to the stock unit, the mod greatly fleshed/filled out the midrange, and significantly smoothed out the highs. The bass also has more weight. Dynamics are improved overall. Generally it's more relaxed and musical (less hi-fi sounding). Avnut's comment about the unit "not being in a rush to deliver" sums it up well. IMO one consequence of this is that the lowest bass is a bit warmer (a slightly rounder leading edge on low bass transients), but some people may not even notice this.
In my system I recently compared my modified 850 to some newer CD players such as Levinson 390S and Aero Capitole 24/192 (both with analog volume control), and I still prefer my GNS-Wadia for its combination of accurate timbre, transparency, and midrange warmth. In conclusion, I'd say go for the mod of your 830, or buy a used Wadia 850-860-861 and get the mod (then you get a better transport mechanism than found in the 830).
In my system I recently compared my modified 850 to some newer CD players such as Levinson 390S and Aero Capitole 24/192 (both with analog volume control), and I still prefer my GNS-Wadia for its combination of accurate timbre, transparency, and midrange warmth. In conclusion, I'd say go for the mod of your 830, or buy a used Wadia 850-860-861 and get the mod (then you get a better transport mechanism than found in the 830).