TL;DR: use a computer, which will provide backups of content, if nothing else
On the USB port, the 84+ and its derivatives (84+SE, 84+Pocket.fr, 84+CSE, 82A) use the same high-level protocol, officially named "CARS", as the TI-eZ80 series (83PCE / 83PCEEP, 84+CE, 84+CE-T / 84+CE-T PE, 82AEP). However, the newer models use larger buffer sizes, some more file types, etc.
So at best, you might be able to transfer a subset of file types and file sizes through direct connection between these classes of models; two successive transfers with the computer as an intermediary fix the buffer size issues.
The 89T also speaks CARS on the lower level, but when TI released the 84+ series a year later, they used minor protocol differences in nearly all packet types, causing near-complete effective protocol incompatibility between the 89T and the 84+ series (and a decade later the TI-eZ80 series). Of course, since there's complete incompatibility on a file format level as well, it made some sense not to make these models willing to talk to each other.
A mini-A male <-> A female USB OTG cable makes it possible to mechanically plug the SilverLink onto the newer class of models, but:
* I don't know whether the USB port provides enough power to supply the SilverLink adequately;
* third-party ASM programs would be needed to deal with the SilverLink at all, AFAIK;
* third-party ASM programs are also required for implementing the variants of the "DBUS" protocol used by the older models on their 2.5mm stereo proprietary jack port.