If the switch didn't work (it wasn't ever a sure thing), then a modchip would still fix that old box. Since you're
buying one, why not stick it in your former system, use that to bypass FlashBios, flash the TSOP with something that actually renders the console usable, then take it out?
You could then stick it in your new box and have two working, modded systems. Link them and play eight player Halo or something, maybe even sell one off and see if you can make a profit.
Just to be certain you're clear on this, you did manage to flash your TSOP - multiple times - However, where you went wrong was flashing FlashBios on there.
Most X-Box BIOS types you'll find are illegal, see. They use parts of the MS BIOS and so break laws. Hence modchip makers can't sell chips with, for eg, the X2 5035 BIOS ready installed.
FlashBios is a legal BIOS built to help solve this problem. It's a BIOS flasher in the form of a BIOS. A modchip seller can legally pre-load it onto his chips, and when someone buys them the first thing the console will have them do is put a new (more practical) BIOS in. Whether the new BIOS is legal is not the seller's concern.

So what you've done is used flashing software to flash this flashing BIOS into your TSOP. Since it's designed to flash modchips (as opposed to TSOPs), you can't use it to remove itself, and because it's designed to
only let you flash modchips you can't load your software flasher again.
If you can make your console boot with another BIOS, that problem goes away... The switch didn't work (for whatever reason; likely your TSOP just didn't have another BIOS in it), so you can use a modchip instead. A modchip essentially over rides your TSOP when you boot the console.