Update:

external PCI idea seems to work, Win98 sees the new PCI Bridge, and sound card, not tried the output, need to disable the onboard sound(I'll try that when I get a bit of time), this could open up new avenues with large Externa GPU's or decent sound cards or PCIE cards if there are drivers for win98.

Ok if the Ood made computers!
My creative Audigy sb0090 works with the T5720. Shows the power is the issue with upgrades, now need to find a cheap 3DFX card!

update:
sound cards work a treat, but gameport seems unresponsive on blaster and CMI card, no matter what I attach, it's not connected, Gameport works fine elsewhere so not a faulty card.

nothing on device manager saying there's an issue, just it's emulated.

second pci port causes issues if used, need some light shed.. may be bios limitation.

This is great - I thought for sure after reading the first post that going PCI to PCIe to PCI would never work but you actually get sound! Whoa!
I can't tell from the photos (maybe that's an ATX PSU connected to the SATA power input of the dual PCI board? Did you manage to power up the PSU with a power button?) but this extra power might be required for the PCI cards to work correctly. Perhaps also on the thin client there could be a onboard dummy gameport using up the gameport address.

For some soundcards to work properly with the T5720, you need the original riser and to populate the original riser with the missing capacitors. (This is probably not necessary if you are using the PCI -> PCIe -> PCI adapter setup as you should be getting proper power and filtering through the adapter.)

See here:
Low volume out of Cobra AW744L II card

One other thing. Going from PCI to PCIe and then back to PCI, I am pretty sure that you are going to run into problems with quite a few soundcards.

I have tried one of those PCIe to PCI adapters like you have there and they are pretty limited in what they work with.... maybe it is better when you are starting out with PCI.

I am also almost 100% sure that the second PCI slot is not going to work with that setup. Pretty sure the motherboard or maybe the BIOS is only set up to handle one PCI slot ID.

I did acquire some PCI risers that have a special chip on them that looks like it will probably allow multiple PCI cards even with the T5720 from what the datasheet says but I have yet to try them out.

There was reports of somebody have a dual riser that they got working with 2x Voodoo 2 cards but there were no details about what the jumpers on that riser were set to. I have one of what I believe to be the same riser, but the ribbon cable is damaged so it doesn't work.

Yes, it's a atx psu with a bench power supply break out board that has a power switch, ordered a pico psu to get the size down.

Few mistakes while messing about, forgot to turn the psu on but it come on it's self, also forgot to plug it in once, but sounds came out so the must be some power from the pcie, but wouldn't recommend it, few people have smoked these pci bridges.

I'm using 3.3, 5 and 12v on the sata connector . I think there s a pin on the 3.3v that may be involved in the turning on of the psu

Had no volume using the onboard pci , hence looking at this as an option.

When using the second slot , some time sees the card, sometimes not, so unreliable tried a PCMCIA adapter card, drivers installed then it vanished.

No other gameport showing on the device manager. Onboard sound disabled, all the usual steps taken. I'll check on my compaq to see if there are diffrent setting for the gameport.

UPDATE,

Tried fresh install, so there are no other sound card drivers present, still Gameport not working. Run out of ideas, even an analogue joysticks not being seen, must be something in the firmware. Project scrapped. Need the port working for the joystick and wheel.

there seems to be a issue between Via and M'soft Force feedback, non compatibility, which was never fixed by either side.