Yes, you can but with a few caveats depending on your particular use case and workflow. Although we generally recommend that the Sphere plug-in always comes first in the effects signal chain, other effects can be used ahead of Sphere as long as exactly the same processing is applied to both channels and the processing is not obviously distorted or non-linear.
For analog processing, such as EQs and compressors, the matching between channels is not necessarily accurate enough when used before the Sphere plug-in, but it will depend on the particular equipment you have. For compression it is essential to enable channel linking. It is also advisable to test your equipment by passing through sine and noise signals and see if the levels remained matched. For outboard digital EQ and compression mismatch between channels is unlikely to be an issue as long as channel linking is enabled for compression.
Another option is to place outboard effects after the Sphere plug-in by creating an analog insert point in your DAW. This has the advantage the output of the Sphere plug-in is mono so channel matching is a non-issue (unless you're using Sphere 180). It also means you only need to use a single channel of processing of instead of two.