Sorry if it wasn't really clear, Sure HSERIn is appropriate where SERIN it's not really to reach the baudrate you want @4MHZ.

The internal USART also offer you the Interrupts where the software SERIN,DEBUG don't

Usefull when your software have to do something else than wait... Even the Timeout of SERINx may be used but with the MIDI baudrate i can't say you'll never miss any character.

HSERIN within a ISR is the way to go.

The Kees Reedijk example is something to play 'round.