DACs and audio formats

I have been reading up on DACs and the formats that they play and have certain questions if someone would care to clarify, please.
1. I have mainly been using CDs and SACDs. Though there are many DACs that handle 24/92, does it mean that they "upsample" the CD data?
2. I see that some top-end DACs are sporting DSD capability. I know that you have to have DSD file to send to these DACs either via a computer USB or via a DVD disc on which the file would reside. But what about the SACDs that I have? Will I be able to play my SACDs using these DACs?
3. Assuming that there are DACs that can play SACD streams, what transports are available to do this?
4. Some DACs that do not do DSD do have USB. Can these DACs be later upgraded, via firmware, to play DSD files? Yes, I do understand that if their "base chip" cannot handle DSD, then these DACs will not be able to play DSD. But what about those non-DSD DACs that might have DSD capable chip? Or a player like Marantz SA-11S3 that cannot do DSD files currently but have USB and DSD capable chip.

Probably novice questions, but I have ignored computer audio long enough. I have been thinking of replacing my aging Marantz player with a new SACD player(like the Marantz SA-11S3). But a discussion with a colleague, who is coming back into audio after 15 years, got me thinking about the DAC route.
Thanks!