One relatively inexpensive way a gamma-ray imaging system can be upgraded is by updating the read-out electronics system and, as a consequence, modernizing the digitization and data-processing methods. The objective of this project is to replace the front-end electronics of modular gamma-ray cameras utilized in multiple small-animal PET and SPECT systems developed at the University of Arizona within the last 20 years. We have previously presented the new front-end board, which utilizes 1-bit sigma-delta modulation (SDM) for energy estimation and a non-uniform 2-bit SDM architecture for timing estimation and triggering. One advantage of this digitization method is that instead of ADC integrated circuits, only a few analog components per channel are utilized, which reduces the complexity and power consumption of the system. The board also includes, among other resources, a Xilinx FPGA combined with an ARM-based processor, DDR3 SDRAM and QSPI flash memory. This project presents the comparison between the original and the new SDM-based front-end electronics board, implemented in a 9-channel modular gamma-ray camera, by obtaining the spectrum of each individual photomultiplier tube (PMT) with both front-end boards. The results show an improvement of 1.5x to 2x in the PMT spectrum resolution with the new approach.