OK, so maybe I'm not the most tech savvy of gamers but I should be able to download and import ROMs for Atari 2600 games, especially as I have two emulators. To be clear I CAN download and import most commercial games from back-in-the-day, with a few exceptions. Mostly a handful of games from 20th Century-Fox and SEGA. But I've had ZERO success with homebrews and WIPs. Since a user at http://highscore.com/ submitted a score for Abyss of Chernobyl: 90 Seconds I've been wanting very much to play it. I have no idea if it's getting a physical release. I hope so. 

A factor to consider is that I have Doxillion Plus on my PC, which I use to archive all of my ROMs. I download the ROM that I want, and extract it with Doxillion Plus into the Folder of my choice.

EMU7800 Version 2.2 (Core 1.4)

Once downloaded I import the ROM file into EMU7800. This emulator will import most everything from back-in-the-day, but fails when it comes to some Fox and SEGA games.

Stella Version 6.0

Has a ton of ROMs already, but whenever I try to download ANY homebrews, regardless of if they're a WIP or are finished games, Doxillion Plus pops up and I get an error message that reads (as an example) The file "Abyss0.19NTSC.bas.bin" cannot be loaded because its format is not supported in Doxillion Document Converter.

What is the snag, and if I purchased a Harmony Cart what steps are involved in downloading ROMs into it? Abyss of Chenobyl is a large game. 64k I believe. Does the Harmony Cart have a size limit as far as individual games are concerned? I performed a search for the Harmony Cart at the AtariAge store but couldn't find it.

Any help would be appreciated.