Ok, let's clarify the 3 things that are most relevant here:
1) Your BC-346XT is an analog only scanner, it will not decode digital communications of any kind, so that means you cannot monitor any APCO P25 transmissions of any kind (well, you can monitor them but all you'll hear is the digital data stream which can sound like static for many people with untrained ears). The S.N.A.C.C. system here in Clark County is not a P25 system - that P25 aspect is currently in limited testing so it's not what you should be focusing on. You should be focusing on what kma371 posted above, that link will get you the info for the actual S.N.A.C.C. system itself - the P25 aspect in testing is only one particular talkgroup with a very minor amount of traffic. According to my most current Unitrunker S.N.A.C.C. data, there are 217 talkgroups on the S.N.A.C.C. system (that I've detected myself) and only one of them is using P25, again the College of Southern Nevada - that's it. There's only 1 talkgroup using P25 comms out of 217 which means 216 of them you can listen in on easily.
There is a S.N.A.C.C. P25 system, yes, but it's a subset of S.N.A.C.C. itself, and no you can't monitor it even though it's just that one talkgroup currently.
2) The P25 system in testing is a small part of S.N.A.C.C. itself, so again you want to focus on getting the actual S.N.A.C.C. system info, control channel frequencies, and talkgroups into the scanner so you can monitor what's available aka the 216 talkgroups you can listen to.
3) The Las Vegas Metro Police Department uses a different radio system known as OpenSky and it cannot be monitored by any scanner or receiver on the market today, period - it doesn't matter if it's analog or digital, you simply can't listen in.
The only police traffic in our area we can monitor is North Las Vegas Police, Boulder City Police, and Henderson Police and they are all part of the S.N.A.C.C. system and yes you can listen in to those. It's just LVMPD that nobody can monitor anymore.
But this is getting off being BC-346XT related and more into our current local systems so, this should be enough info for now, ask in the Nevada subforum if you need more help.