Official Website.

http://snesmusic.org/

Lossless quality, as they are the very original music files you find in the carts of the games themselves.

Playable with SNES SPC700 Player (the best one there is).

Sorry to rain on your parade (although 2 weeks later). First: it is not its native format, is a data rip. The SNES doesn't manage natively .spc files, it manages SPC instructions plus samples. Second: it is not lossless, the quality will vary depending on the SPC emulator program and its settings not to mention that it is EMULATED.
To achieve real lossless for SNES/SFC music, you have to record directly from the SPC chip (i.e. the SNES audio output) itself.
It's the same problem with .nes, .vgm, .psg, .psf, .gym and any other emulated sound format. They are good for occasional listening but not for audio preservation.

You can convert those data rip files to .flac, but is really dumb to make 14 MB/tune from a tiny ~2 MB file.
No offense, but no wonder why no one has replied before me (though I'm pretty sure who's been busy ripping from that archive about 2 weeks ago following your suggestion).

As far as I understand it, the SPC format for SNES music is very different from NSF for NES music. SPC is captured from RAM while emulating a game, but NSF is an edit of the ROM where they throw away everything except the audio data (sort of like cropping a picture). I don't know about the other formats you mentioned, but they all end up working in a similar way to traditional tracked formats like MIDI or MOD.

This means they end up relying on emulated output if you're playing them back on a computer. So technically the audio output is lossless, but not accurate (though to most people's ears the level of accuracy in emulation these days is indistinguishable from the original).

If you're a total audiophile purist, I know of at least one way to play back NSF files on real hardware (loopy made a player for bunnyboy's PowerPak at retrousb.com). I don't mess with SNES as much, but there's probably something out there for that too.

At the end, it's a matter of taste: if your VGM files sound good enough to you, then you'll enjoy it. If you wanna take the extra effort to setup the hardware and such, it's good too. To each their own.