Bookmark the books you want to switch back and forth between - even if you just bookmark the first page (the Reader will remember your last reading location, even if you switch to other books).
Then, rather than going to the TOC to find the books, go to Notes. I left my 600 at work, so I can't remember the exact key order...it's something like Notes > Bookmarks. Pick whichever book you want to read.
Then, to switch to a different book, use the "Back" selection, rather than Home. You'll go back to the list of bookmarks.
Delete the bookmarks when you've finished reading, to keep your list short.
I actually bookmark the books I finish...that way, I can add them to be "finished" list later on. But I think this would work for you without a lot of extra keystrokes or frustration...
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