Media Vision's Pro AudioSpectrum/Plus/16 cards include a PC-speaker output header, to which you can connect an internal speaker (either the one already in the system, or one entirely separate). If the wire leads from the speaker in your T5200 are too short to reach the card, I'd suggest using a 2-pin header piece as an interconnect between its connector and that of another 2-pin cable, as a means of extension.
The speaker header on the mentioned PAS cards is of the switched variety, meaning it's only active when nothing is plugged into the 1/8" speaker/line output. Additionally, these cards provide onboard shadowing of the 8253 (PC speaker) sound generation of the host system, resulting in one less cable to run. This feature is mostly non-functional in 486+ systems, but should work well in your T5200.
I'd suggest a MVD101-"D"-bearing PAS16 card, which can even be installed and configured for use in the 8-bit slot of your system, leaving the 16-bit slot free for something else. This particular variant includes jumperless configuration of the SB-compatible portion of the card, and MPU-401 (UART) compatibility.

Interestingly enough, early Tandy 1000 variants have a pin on the ISA bus that is designed to be used as an audio input into the sound multiplexer. I've yet to encounter any sort of card that outputs sound on this pin though.
NJRoadfan wrote:The WaveBlaster header on Sound Blaster cards has audio output pins you can directly wire up a speaker.
This is news to me. Which card(s), and which pins?