I believe that the "split voltage" you are referring to is the ability to set the I/O voltage and the Core voltage separately.
The Intel P54C processors like your 133MHz Pentium used a Core voltage of 3.5 volts. The I/O voltage was also 3.5 volts.
Therefore, the motherboard's voltage could be fixed at 3.5 volts.
The Intel P55C processors like your 233MHz Pentium MMX used a Core voltage of 2.8 volts and an I/O voltage of 3.5 volts.
Therefore you need to be able to set the Core voltage (VID) and the I/O voltage (VIO) to different voltages, hence "split voltage."
Since you indicated that your motherboard has a VRM (Voltage Regulator Module), I would assume that you can set the Core voltage to a lower value.
I can't say for sure because I don't know what motherboard or chipset you have.
If you need a more definite answer, post more information about your motherboard and I will try to help.
I need motherboard manufacturer, motherboard model number, and chipset type. I also need to know if you have the motherboard manual.
Hope this helps. Good luck.
John