agree with fozzy. A standard rackmount UPS designed for PC gear is not what you want for taping. Very inefficient as far as weight-size/power ratio (especially since your gear is DC).
Now, you can build your own UPS specially designed for your gear .. but doing this properly requires a moderate amount of electrical engineering.
Have you considered simply buying a large SLA battery (these come in 6V, 12V or 24V versions)? Look for the deep cycle versions. You´ll also need an accompanying sla gell cell charger.
If 6-12-24 isnt what you want, or you need a combination thereof. Take a look at ´car computer´ power supplies. These voltage regulators and converters are usually capable of 5V, 12V and 19V outputs and will make sure your battery isnt sucked dry (creating a memory issue). You might want one of these regardless if the SLA gives the voltage you need. Keep in mind a battery´s voltage will change during discharge, and a regulator like this is designed specifically to output a steady voltage.
I use UPSes a lot but not for taping. Heavy and ineficient for our purposes. Most have fans and non-efficient AC transformers. Good if you are powering from a generator or need temporary diconnect from the grid. If you are looking to power taping gear I would got the SLA + automotive AC inverter
FWIW: every 5000KVA UPS I have seen uses SLAs