Going by the datasheet, the REGADR is 5bit wide, bit4 is don't care for the "Xnh" registers. Some of the "Xnh" registers are referring to the "current sector" (that from most recent DECINT interrupt), and there can't possibly be TWO different "current sectors", so bit4 is really not selecting anything in that cases.
The six buttons and LCD panel are probably only for playing Audio discs without TV set connected, which would be a rather unlikely/unimportant scenario for a SNES emulator. Games might be able to completely disable that stuff via the mechacon "Key Ignore" commands (assuming the command is related to the buttons).
The new APU might make sense if it has more extras, like PSX-style stuff with 24-channel audio or better echo, then it would have been worth the effort to put a new APU in expansion units (though such features might require more Sound RAM to be of any real use).
The missing extra CPU power could have been solved by just using a BIOS cart with coprocessor (as done by various SNES game carts), so that could have been implemented without problems without needing to change the CDROM drive hardware. Even with the fastest coprocessors, the main bottleneck would have been squeezing possible highest-quality graphics through the SNES PPU hardware.
And, even with my fifteen year old PC, I've defeated all those photo sharing sites for multimedia quadcore smartphone generation artists... studied all the hardware photos at their creative viewing angles and their insanely low and insanely high resolutions... wondered how often the photographers have stumbled over their own feet... and, anyways, here's my first guess on the component list:
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Sony Playstation SFX-100 Console - Component List Mainboard IC101 100pin Nintendo S-CPU, 5A22-01 (65816 CPU with joypad I/O ports) IC102 100pin Nintendo S-PPU1, 5C77-01 (Video Chip 1) IC103 100pin Nintendo S-PPU2, 5C78-01 (Video Chip 2) IC104 28pin NEC uPD43256A6U-10L? (32Kx8 SRAM, Video RAM 1) IC105 28pin NEC uPD43256A6U-10L? (32Kx8 SRAM, Video RAM 2) IC106 ... whatever, maybe S-ENC IC107 64pin Nintendo S-WRAM (128Kx8 DRAM with B-bus) IC108 28pin 65256BLFP-12T (32Kx8 SRAM, Sound RAM 1) IC109 18pin Nintendo F411 (NTSC CIC) IC110 28pin 65256BLFP-12T (32Kx8 SRAM, Sound RAM 2) IC111 64pin SONY CXP1100Q-1 (APU, some newer S-SMP revision, SPC700 CPU) IC112 80pin SONY CXD1222Q-1 (APU, some newer S-DSP revision, Sound Chip) IC113 20pin LC78815M (Two-channel 16bit D/A converter 1) IC201 80pin SONY CXD2500AQ (CDROM Signal Processor) IC202 20pin LC78815M? (Two-channel 16bit D/A converter 2) IC203 48pin Noname ... maybe Servo Amplifier (like CXA1782BR on PSX?) IC204 80pin SONY CXD1800Q (CDROM Decoder/FIFO, equivalent to CXD1196AR) IC205 18pin 74xxxx? (PCB has 20pin solderpoints, but chip is only 18pin) IC206 28pin SONY CXK58257AM-70L (32Kx8 SRAM, CDROM Sector Buffer) IC301 8pin Texas Instruments RC4558, "R4558 TI 25" (Dual Op-Amp 1) IC302 ... ... whatever, maybe one of the 8pin IC???'s IC303 8pin Texas Instruments RC4558, "R4558 TI 25" (Dual Op-Amp 2) ICxxx ... if any... ? IC??? 8pin whatever (front board edge, near headphone socket) IC??? 8pin whatever (front board edge, near headphone socket) IC??? 24pin whatever (front/mid board edge) (probably S-ENC or so) CN201 29pin To LCD Board CN.. .. To CDROM Drive CN.. .. To Controller Ports CN.. 62pin SNES Cartridge Slot CN.. .. Rear panel Daughterboard with LCD IC701 80pin NEC uPD75P308GF (CDROM Mechacon?) IC7xx ... if any... ? X701 oscillator CN701 28pin LCD and six Buttons (28pin, or maybe 2x28 pins?) CN702 4pin to somewhere (2 LEDs ?, left of drive tray) CN703 29pin to Mainboard (29pin, or maybe 2x29 pins?) CN704 3pin to front panel (disc eject button?, right of drive tray) ICxxx ... if any... ? N/A? 28pin Something like BA6297AFP,BA6398FP,BA6397FP,AN8732SB,etc ? Daughterboard with controller ports ??? ... whatever Daughterboard with Eject button ??? ... whatever, a button, and maybe more stuff for the 3pin wire Daughterboard with LEDs ??? ... whatever, two LEDs, and maybe more stuff for the 4pin wire Components in actual CD Drive unit ??? ... whatever External Connectors 2x controller ports (front) 1x headphone port with "level" regulator (front) 1x "NEXT" port (serial link like PSX maybe?) 1x Audio R (red) (apparently with mono-switch when not connected) 1x Audio L (MONO) (white) 1x Video (yellow) 1x S VIDEO 1x RF DC OUT 1x MULTI OUT 1x DC IN 7.6V BIOS Cartridge - Case Sticker "'92.10.6." (plus some japanese symbols) PCB "RB-01, K-PE1-945-01" IC1 64pin Nintendo S-WRAM (128Kx8 DRAM) IC2 64pin Nintendo S-WRAM (128Kx8 DRAM) IC3 32pin HN2xxxxxx? (Sticker 0.95 SX) (ROM/EPROM) IC4 28pin SONY CXK5864BM-12LL (8Kx8 SRAM) IC5 16pin Noname? IC6 14pin 74F32 (Quad 2-input OR gates) IC7 16pin 74F138? (1-of-8 inverting decoder/demultiplexer?) IC8 14pin Noname? IC9 14pin Noname? IC10 16pin Noname? IC11 16pin Nintendo D411 (NTSC CIC) ? ? white space (in upper left) ? 2pin something with 2 pins is apparently on PCB back side (battery?) Note: The date codes on the three S-WRAM's, D411, and uPD75P308GF seem to be from 1991. Sticker on case of BIOS cart seems to be from 1992.