Driving threaded inserts - Sawmill Creek Woodworking

I'm working on driving threaded inserts into hickory table legs to be used to secure the legs to the table. I bought the ez-lok 1/4-20 303 stainless inserts for hardwood and the associated driving tool. I drilled out the holes with a 3/8 forsner and then reamed them to the 25/64 (what the manufacturer recommends) with a twist drill. I started them in the drill press turning the chuck by hand as I pushed the quill down. They all started just fine in the holes. I then used my impact driver to try and drive them home. The first leg went in perfectly. The second leg I ended up breaking the slots on the threaded insert and had to carefully back it out so I could replace it. I then noticed that the driving tool was a pretty beat up, like the impact had done a number on it (are these tools meant to be run with an impact?). I'm now waiting on replacement parts to ship from rockler - 2 driving tools and some more inserts so hopefully I can get them all driven. Are there any tips to getting these things to drive home successfully? Its been years since I last used a threaded insert, and I had forgotten about putting wax on them before driving them, so I will definitely be doing that. I'm debating if I should upsize the holes to 13/32 since this hickory is tough stuff, or at least in the legs that are giving me trouble - they drove in smoothly into the first leg and were really fighting on the second leg before they broke. Anything else I should be doing?

Another way to drive them that would avoid the issue with the slots getting messed up is to cut the head off an appropriate size bolt and chuck it in your driver. Then spin a nut on the threads followed by the insert. Thread the insert on most of the way, then tighten the nut down onto the insert. Use this to set the insert. I would definitely wax the threads, and if it is still a real hard go then I would go a wee bit bigger on the hole diameter.