LAME has just been added to Fedora 25 and newer (still in updates-testing with buildroot override in place). sox can use this for MP3 encoding support by adding BuildRequires: lame-devel to sox.spec.
https://koji.fedoraproject.org/koji/taskinfo?taskID=19595414 Testing would be appreciated.
f26: https://koji.fedoraproject.org/koji/taskinfo?taskID=19595735
sox-14.4.2.0-9.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-5cb6bf4b59
sox-14.4.2.0-9.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-5cb6bf4b59
sox-14.4.2.0-9.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.