Hi Rochabian,
Thanks a lot for posting this. I'll have a look at ToastyX's method and keep an eye on it.
Indeed I have the 5xxx and higher models working with low resolutions here for some months already, using the ADL api over patched drivers to remove the limitation, so I guess it's the same thing he's done. However, there're extra modifications that need to be done to allow dynamic modelines in the way that GroovyMAME uses them. ADL allows dynamic modelines but it's very slow in practice to be usable with stock drivers and GroovyMAME, so some patches are required. Besides, you need to remove the limitation of 10 custom modes.
Currently I'm in the process of adapting VMMaker, Arcade OSD and GroovyMAME to use these new methods, which is taking some work.