Of the default patches so far I like Fantasia Horns and all the orchestra hits are nice and rich.

• Patch demos: https://www.synthmania.com/jv-880.htm

There are different kindas of expansion cards available, but they're all pricey.

• Roland Expansion Board cards are added through a hole in the top of the uni. They also work with other Roland ROMplers (JV-, JD-, XP-, XV-) though not all are compatible across all machines. It sounds like the patches on the 97-99 demo boards don't work with the 880.
  • There's also the Sector101 SR-JV Romulator, which is a rewritable card that fits in the same slot. A card and the writer together cost about as much as getting one official card.
• There's also a slot on the front for PCM cards. It seems like the patches are largly duplicated across the PCM and expansion boards.
  • https://soundprogramming.net/synthesizers/roland/roland-so-pcm1-expansion-cards/
  • https://www.sweetwater.com/sweetcare/articles/roland-so-pcm1-so-pcm-pcm-card-list/
  • http://sampodo.la.coocan.jp/synth/jvcard/jvcard.html

• Edisyn https://github.com/eclab/edisyn
  Patch editor and manager/librarian that works with the JV-880 (and lots of other things). Has a Linux version.
• JVTool https://jvtool.sourceforge.net/
  Linux, no Mac version. Maybe has more features?
• JV PatchEd. https://sourceforge.net/projects/jv-patched/
  No Linux version?

• http://www.synthzone.com/midi/roland/jv80/

• https://llamamusic.com/jv880/ - Lots of info.
• https://www.polynominal.com/roland-jv880/index.html
• http://www.muzines.co.uk/articles/breaking-with-the-rack-pack/10518 - 1993 review which covers a lot.
• https://www.sweetwater.com/sweetcare/?s=Roland+JV-880&sc_submit=Search