A Soundblaster Pro is going to work fine in that machine, if you can fit it mechanically. I don't remember the placement of the battery on the riser card exactly, and if it would interfere with the 16-bit extension of the ISA slot, but I am extremely confident that the Soundblaster Pro uses the 16-bit ISA extension only for access to DMA channel 0 and maybe IRQ 10. The Soundblaster Pro supports no kind of 16-bit bus cycles, so the absence of a 16-bit slot is not going to hurt.
You might want to test the raw video write speed. The V30 should be able to max out the 8MHz ISA bus, which likely runs at the XT rate of 4 clocks per ISA cycle, so the maximum transfer rate is 8MB/s. I don't know about the VGA Wonder, but I tested several VGA cards in my classic Turbo-XT, and none of the (cheap) 8-bit VGA cards was able to sustain 4 clocks per byte write, but an ET4000 and a ATI mach32 ISA were. If you get less than 2MB/s raw write speed, you might want to test a more modern 16-bit VGA card. Contrary to the soundblaster pro, not all 16-bit VGA cards work in 8-bit slots. For example, only two of my three ET4000-based cards worked in my Turbo XT.
Expanding the ISA bus to more slots does not need any logic. But classic TTL chips work in a way that you need to actively draw power from the input pin to make it zero. The mainboard is only able to draw a certain amount of power, so there is an upper limit of TTL chips you may connect to the mainboard until the logic low level gets weak and the system gets unstable. This is much less of an issue if you use expansion cards with modern CMOS-based chips instead of classic expansion cards with TTL chips. The official IBM specification for the ISA bus is "two low-power shottky TTL chips per slot on each ISA signal", and they hit the mainboard limit on the XT. Only seven of the eight ISA slots on the mainboard are directly wired in parallel, whereas the eight slot is driven by a separate logic amplifier (buffer) chip, which needs a special control signal to activate, which is supplied through the reserved ISA bus pin B8. The PS/2 drives the ISA data lines using 74ALS245 chips and the address lines using 74ALS573 chips, which are more modern and definitely strong enough.
The PSU might indeed pose a problem, depending on the load the cards pose on it. You can estimate whether a card "draws a lot of power" by checking whether it gets warm. The Soundblaster 2.0 might take some power for the built-in speaker amplifier. The EMS card might use a considerable amount of power depending on the technology used for the memory chips. 2MB on a half-sized card sound like a modern CMOS-based design, so most likely it is fine, too.
Possible upgrades for that system includ
- a TNDY sound board. As the PS/2 model 30 mainboard does not have the AT-class 16-bit DMA controller, the port range for the tandy sound chip is not claimed by the board. If the board drives addresses below 100h to the ISA bus, you could get tandy compatible sound at the hardware level. The schematics are not helpful for this question, as the decoding process for the "BG L" and "BG H" signals that connect the data lines on the ISA bus to the processor are generated by a custom IBM logic chip, so it is not obvious if they go active for the mainboard I/O range (00h..FFh).
- an MDA/HGC clone card to obtain a dual-monitor system
- a 1.44MB capable floppy controller (but then you need an adapter to connect that controller to a PS/2 floppy drive)
