This combo is reputed by those that use it, and similar systems, to be particularly good. I have a Pioneer DV-79AVi ( 989AVi) and a Sony TA-DA9000ES, and even to a pair of critical ears that think my old Denon AVC-A1D sounds poor, I reckon it's a great sound every way you look at it.
The DVP-NS9100 is one of the best sounding "universal" players, and is considered to sound as good as the SCD-XA9000 when used over i-Link, which is saying something.
The DA7100 is a good partner, but anecdotal evidence is that it should not be used with low impedance or especially reactive speaker loads. Otherwise it's fine.
An all-digital signal process is very appealling, but it's surprising how much of a contribution the i-Link makes. It sounds much better than SPDIF, and I suspect there is a lot of synergy in this SOny combo.
Nick