Guru dumped Metal Slug 6 for Atomiswave, and with a little help from Cah4e3 I got it going in MAME.

Here’s a set formatted and partitioned blank Mac .CHDs you can use to install System 6 or 7 following the instructions on the MESS wiki. We have ’em in a variety of popular sizes: Big thanks to Grégoire Duval who set these up.

v5 CHDs for MESS 0.145u1 and later:
20 MB
40 MB
80 MB
100 MB
700 MB
1 GB
2 GB

v4 CHDs for MESS 0.145 and earlier:
20 MB
40 MB
80 MB
100 MB
700 MB
1 GB
2 GB

Dr. Decapitator recently read out the internal ROMs for the Super NES “DSP-1”, “DSP-2”, “DSP-3”, and “DSP-4” chips. These are all fairly low-powered NEC uPD7725 16-bit DSPs used to offload 3D trig calculations in games like Pilotwings and Super Mario Kart. byuu wrote an emulation core for this chip for bsnes and kindly donated it to MAME/MESS so now SNES in MESS has perfect math on games using the DSP as well. And the great thing is the previous HLE simulation code used for these games was larger than both the 7725 core and the ROMs. So you save a little compile time and memory and get guaranteed perfect results. I love it!