I think the OP might mean a sequencer in the sense of a MIDI sequencer which is why the QY70 was mentioned.
You might have already found your answer in the QY70 / QY100. Are you wanting a "band in a box" type thing where you can create changes / chords for a whole song, and have a bunch of synthesized instruments? Or a guitar trainer to play MP3's to practice one phrase at a time? Or maybe a SMF player where you can just download MIDI files and play along with them?
The problem with the QY70 & QY100 is that they were made in the mid/late 90's so some of the storage cards / transfer methods are out of date. But there also isn't any compact hardware quite like it: compact, all-in-one composing tool (though smartphones are getting there now).
- If you want to play back premade material (ie. MIDI files) you need a computer sequencer or MIDI/SMF player with a built-in set of synth sounds (most keyboards will do this too).
- If you want to write your own chord changes and play with a beat you want an arranger / groovebox / the QY100.
- If you want to play certain sections of songs in a loop, you need a guitar trainer.
The QY70 is unique in that there aren't too many stand-alone hardware boxes do what it does anymore since the computer has taken over (the QY100 is
still in production after all these years).
SMF arrangers & players:
Roland U.S. - DisCover 5M: Realtime Orchestrator QY100 MT-90U: Music Player Guitar trainer these will allow you to load MP3s, slow them down, and typically have a built in metronome, tuner, effects, and are very portable:
TASCAM
If you have a smartphone you may also want to check to see if there are any apps which can play midi files, or arrangers, or guitar trainers that do what you want.
Post back if anyone has gotten close to what you are wanting. I think everyone is a little unclear.