Forgive me if some of this has been covered. Also, I am no expert with converting DSD discs (SACD) to .iso images!
I can tell you that converting DSD to 24/88.2 is a high def to high def conversion and any loss would be well within perception bias. You will get more sound fidelity by converting DSD to 24/88.2 PCM and listening through pro PCM DA converters than listening to the DSD program natively with consumer grade DSD DA converters. So there's that.
I believe Foobar and other apps that convert DSD tp PCM give you the option to reduce the gain. A DSD to PCM conversion can give you data that goes above zero! You can give yourself a safety margin of -6db. Better is to convert the files to 32 bit floating point instead of 24 bit fixed. Then you can lower the gain precisely with a DAW app as needed to end up normalized just under 0db. Then render to 24 bit flac files.
As far as 88.2k vs. 176.4k, 88.2k is a container that can hold the complete fidelity of an audio file. 176.4k can be used for processing work (especially restoration work) and have some better results with the math involved in certain processing. When you're done working on it, 88.2k will contain the complete final result audio with no loss. (Same thing for 96k vs. 192k.)
Well - Jim. Most of what you say there is over my head. Which illustrates why this is all so confusing to me. You say converting DSD to 24/88.2 PCM. As far as I know, there are no options to do that in Foobar. PCM? I dunno. I see Flac, WAV, and some other things that mean very little to me. For me, it really has to be a check the box thing. If it requires understanding what happens if I "do this, or do that" Isn't gonna happen. Unfortunately.