The PLM from Smarthome unfortunately has turned out to not have as reliable of X10 communication as their power line controller. The EZSrve leverages the PLM from Smarthome. In the short term we cannot fix this in firmware.
One thing I did not see you try is place the boosterlinc closer to the EZSrve (to the point where you piggy back the EZSrve on the boosterlinc). The boosterlinc should rebroadcast the signal at the PLC strength.