The Delta 66 is a nice audio card. On the personal studio side, thigns have gotten cheaper, yes... However, when we talk about things that cost thousands of dollars, we are not talking about some old technology that has now been replaced by the M-Audio line of cheap hardware. We're talking about products by companies like Apogee that are really far beyond normal consumer audio products.
Most of the high end boards get around the problem of converters by replacing them (or supplementing them) with digital inputs... for example, the Frontier line, and offerings from Digidesign, MOTU, Creamware, and most other companies offer either S/PDIF digital ins and outs or ADAT digital ins and outs, because on the pro level, outboard A/D and D/A converters are vastly superior to the converters that can be included on an affordable PCI card.
The process of putting together a system that uses professional quality converters and digital clocking mechanisms can easily run into the hundreds of thousands of dollars. That has nothing to do with outdated technology. It's not jsut age, but quality that determines the price stratification in audio gear. The reason there are such expensive audio converters is the same reason that a vintage 24-channel Neve board will always be worth more than a 24 channel Mackie board.
So to answer your question, at the high end I would use either a Digidesign card with a high quality clock source, and
the Apogee AD-8000 converter with the AMBus Pro Tools interface, or a Creamware Pulsar card with the Apogee AD-8000 and the AMBus ADAT interface, and a high quality clock source, or a MOTU 2408 with the Apogee AD-8000 and the AMBus ADAT interface.
Any of these systems will run you 6000$ just for eight converter in channels... to get 8 outputs you'd add another $1250. Then add your audio card, for around 2-3000$, and a nice clock source for 1000$ more. And it never really ends...