Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.
Download on the App StoreAudiobus is the app that makes the rest of your setup better.
iOS App suggestions for live performance
I have an iPad Pro, all the gear to hook it up to my PC, and I use Reaper on that PC. I own several hardware synths and enjoy lots of different styles of music but one I haven’t performed any of ar all is electronic music. Like many of you I have a lot of soft synths and iOS apps. I just don’t use them enough 
After coming to the conclusion that it seems a bit silly to buy a hardware sequencer For doing some live at home electronic music jams, when I can start much cheaper and more flexible by using iOS apps I did some research but am a bit stuck.
I am envisioning a combo of hardware and software synths controlled by the iPad in some fashion but in such a way that gives a lot of the same functionality of using something like Ableton and/or hardware sequencers etc.
What really intrigues me is the ability to have everything synched up but just a few control points on the iPad or a usb device controlling the iPad.
I should also mention I have AUM and AudioBus as well.
What iOS apps give the flexibility to control multiple midi devices and create and control sequences in real-time easily (kind of like in Ableton or MPC / Launchpad etc) Using “scenes” etc?
I’m leaning towards beat maker with a sequencer app like thesys
Comments
Should I perhaps be looking at Drambo?
Drambo is a good choice.
Modstep is too, though it's a bit of a head scratcher (odd interface), hasn't been updated in a long time. It really works well though if you only think of it as a MIDI sequencer and don't try to host apps in it, but host them in AUM or Audiobus and/or use it to sequence hardware.
Zenbeats is pretty good too, but I'm not sure how well it handles midi externally, that's not really what its designed mainly for.
A combo of Drambo and LK midi controller would take you really far
Testing out LK this evening.
Quantum offers 6 sequences of up to 64 steps each with lots of options:
https://apps.apple.com/gb/app/quantum-sequencer/id1207932898
I'd first ask what kind of sequencer you look for, but for live use and as you look for LK, I'd expect scene-based (e.g. Ableton Live-like).
Unfortunately, on iOS there is a a lack of really good scene-based live sequencer, unlike Xequence which is really good, but only linear.
No one yet mentioned BeatMaker 3 (only if you meant it by your meantion of "beat maker"). Their scene based mode of sequencer is also quite nice. If you don't mind triggering the scenes / clips from touchscreen (they're not MIDI mappable, although you can MIDI map triggering the whole scenes). The piano roll is not the best on iOS, but still decent. They reportedly focused on MIDI clock timing in recent updates, so it should be fine to use with hardware, but it's better to find someone with real experience.
I have just recently tested demo of LK, it also looks pretty good, but can't tell the real-life experience. But you should be able to test it with demo mode with hardware too.
With modestep I have mixed feelings, every time I tried to use it as a sequencer for other apps, I was only frustrated. Can't tell specific thing, maybe just that the UI is weird and combined with some real bugs, it's annoying to use. But there are happy users out there and they're mostly using it as a sequencer for hardware, so definitely worth a try. Also, it has a very nice feature of triggering PC MIDI command = super useful.
Last but not least, there are some solutions for scene-based sequencing written in Mozaic, which can be hosted in any AU host, but preferably AUM or Audiobus 3. It gives you huge flexibility and can be tailored to your taste, if you don't mind getting your hands dirty with some code
And if you don't mind spending 95% of time writing code and 5% with music in the end (and still not be happy with it, I am the living example 
)
Be prepared for a bit of frustration, live sequencing is the toughest part. I am trying various options for several years already (but I want to use iOS apps only + MIDI controller), I am observing and talking with people who play serious live sets from hardware and I can see there is no one-for-all recipe. Except that it takes a lot of preparation and a lot of compromises you need to make. Even if you are using hardware only, with multiple machines, the orchestration between them is a tedious work.
Zenbeats has a cliplauncher, but i don’t know how it performs with external gear.
Works well, the only drawback is the lack of CC with external devices
Beatmaker 3 has good MIDI sync now.
On top, the following apps are my choices for combining with hardware MIDI clock:
Genome Midi for launching MIDI clips live on different MIDI channels
Groove Rider GR-16 for samples, sliced loops and a great wavetable synthesizer.
Korg Gadget also follows MIDI sync well.
As does Loopy HD in case you also want to do live looping.
Actually Korg Gadget is an interesting tip. I actually really like their pattern based sequencer. It's not that powerful as Ableton Live for things like number of repeats, follows etc, but still easy and fun to use. If they work well with hardware, I'd really give it a try.
Xequence2 will sequence external devices as well as other apps, incl. Korg Gadget. It ships with pad and drum maps for many devices.
I'm not sure about its UX capabilities for triggering its own sequences.
In using LK - can anyone help me w/reducing the velocity/volume on notes in the sequence - I am not seeing the display act like the display in the referenced page on their website. Maybe that only functions in Ableton mode and not standalone?
https://www.imaginando.pt/products/lk/help/matrix
I see the piano roll full screen but there is no space at the bottom for the red volume/velocity bars to even show, let alone the bars themselves
You need to click a key on the keyboard to the left. Then you can adjust the velocities for the notes which fall on that key....