Hello Cordelia.
Your are right: the message corresponds to a clash between a 64-bit system trying to use a 32-bit library. The Antescofo Linux/PD version has been compiled for 32 bits. We have 64 bit version for Mac, but we do not have an easy access to a Linux 64 bit environment. We will try to find one, but it will take some time.
The modern 64 bits processors are fully backwards compatible with 16-bit and 32-bit x86 code. So, in the mean time, you can try to install the 32 bits version of PD on your 64 bits system. For instance, on Ubuntu or Debian, the so-called “Multiarch” makes this relatively easy cf.
why-does-my-64-bit-system-look-for-32-bit-repos/
how-do-i-run-32-bit-programs-on-a-64-bit-debian-ubuntu
When you have a 32 bits version of PD running, it should accept the Antescofo object (perhaps you should install the ia32-libs compatibility library if it not already done).