If one intends to sync up acoustic instruments (like your guitar) or vocals with sequenced MIDI compositions on the Amiga, a good way to do this is with an external digital multitracker that has a MIDI port.
I used a Yamaha MD-8 multitrack machine synced to Bars & Pipes for a lot of my music. The Amiga was controlling external synth modules, and any acoustic instruments were recorded on the sync'd up MD-8. Then all was mixed down to a DAT deck (but today you would use any digital recorder or computer).
You can still find digital multitrackers being produced, or just buy a late 1990s or early 2000s model (Roland, TASCAM, FOSTEX, Yamaha), which are going for peanuts on eBay as most people have switched to DAWs (i.e. Protools, Cakewalk, etc.).
The only "catch" is that one needs to make sure that the sequencer software on the Amiga is capable of sending and/or receiving a MIDI-clock or MIDI Timecode (MTC) signal to allow synchronizing.