Hello! Glad you like the improvements and thank you for your support! What you're describing sounds like LYX files to me, these are going to be slightly smaller, the LNX files are just 64 bytes larger and contain a header at the start of the ROM to provide additional information about the ROM. ElCheapoSD expect LNX files and I know there are tonnes of LYX files out there that have a .LNX extension. I'm working on an online utility that will be able to fix your LYX ROMs, will try and get it finished this week. At the moment it can convert 256K LYX files to 512K LYX files, but that won't help you in this case. The utility is here - https://atarigamer.com/lyxconverter. Check back in a few days, hopefully I've had time to update it by then.
Thanks for the reply. The files I downloaded did have the correct extension but it seems they are LYX files in disguise so now I know what to look for I won’t make the same mistake again. I found an archive with most of the commercial releases so I’m just enjoying playing Desert Strike for the first time. Happy Days.
Just need a new screen next : )