The Panasonic KX-TDA3450 card is not available anymore and even you have one -- you can use it with Panasonic KX-TDA15/30 only, not with KX-TDA100/200/600.
Otherwise, you can use the KX-TDA3450 (and eventually plus 3451 for up to 8 channels) for integration of Panasonic KX-TDA15/30 with 3CX -- either via bridge (slave to 3cx) or SIP trunk (without registration). The same applies to other Panasonic IP PBXs (KX-NCP, KX-TDE) supporting SIP trunks.
The other theoretical option is to use intermediate ISDN to VoIP gateway (search the forum - there are some comments), but this is rather complex as setup.