To elaborate on this, Zoe is suggesting you assign cv2 of the a-190-1 to mod wheel-see page 13 of the manual. Which would give you one controllable mod source from within your daw, without spending any money. You could even do some nice lfo morphing if you are willing to put the time into drawing it.
If you have money to spend I cannot stress how great expert sleepers silent way is. It uses the audio channels of your audio interface as cv ins and outs. There are a few options.
You can use your current interface. The software encodes the output to be compatible with your modular, you use the inputs/outputs already on your interface. You either need a dc coupled interface (majority aren't-see their site for compatibility list) or to build special floating ring cables, which are very easy to make. Cheap and easy, but you will only get positive cvs-not really a big deal.
Personally I have chosen to go for the es3 module. This uses one of the ADAT/lightpipe outputs of my interface to send 8 channels out to the modular. These 8 outputs are high resolution and are suitable for driving vcos, sending out software generated lfos, software envelopes and software sequences.
There is also the es4 module, which this time uses the SPDIF out of your interface. This gives you 5 outputs, 2 of which are high resolution for driving vcos, the other three for the lfos/envs/etc. I've borrowed a friends one and it will definitely be my next synth purchase.
The software itself is free to try, so you just need to build a cable or two and give it a go. Its got a 15 minute trial, but you can just reopen. If you buy the hardware you will probably want to buy the software licence to go with it, but some of the more important plugins within the suite have no time limit so you don't need to buy everything at once