Torrents
emissary-cli supports both I2CP and SAMv3, meaning any torrent client that utilizes either protocol should work. qBittorrent has been tested more extensively and provides higher throughput when used with emissary-cli.
qBittorrent
SAMv3 must be enabled in router.toml and I2P must be enabled in qBittorrent. The default SAMv3 TCP listening port for emissary-cli is 7656.
Under Tools > Preferences > Connection, enable I2P:

I2PSnark
Standalone I2PSnark maintained by the I2P+ project can also be used for torrenting. The installer is found under Download I2P+ > I2PSnark Standalone at the bottom of the page. The default port for I2CP is 7654.