[Serusers] Recommend ATA adaptor ?

Hi, Can someone recommend ATA models that work easy with Openser, based on experience? I am currently using Sipura SPA3000 and PAP2 which are highly configurable but at the same time, need much works with trial and error fashion to get them work with Openser, Freeradius, Mediaproxy and CDRTool combination. Especially, I am not quite sure if these are handling "VIA" header correctly. Because setting up Outbound proxy was the only solution I found to get these units send "BYE" to the server, otherwise it will send "BYE" directly to PSTN gateway, resulting forward_reply error, killing a child process and mediaproxy never had a chance to mark "stop time" for acc. Can anyone suggest ATAs that imposes least burden of configuration to work with the setting above? Thanks mush in advance. John K.