i have absolutley no clue what you mean by 4600 portable system.
a powered mixer is ok for just vocals and mayeb some keys. Putting a little guitar in the mix is generally ok with those as well. If i was going to put a pa setup together i would get the best mains speakers i could with stands) and a powered mixer if i needed to save money. 1x12 mans with horns are ok for a lot of stuff, 1x15 mains with horns work better for larger gigs or where you need pa support with bass. Of course, you still have to think about monitors, etc. if you had the money for monitors as well you might ant to think about getting a powered mixer will let you use its internal poweramp to run the monitors, and that will let you run a line to an external, more powerful poweramp to run the mains. then i would buy a couple of small monitors.
not that you need anything like this, but let me put things in perspective for you. My guitar player does sound for other bands as well, and has a decent income. This is what we bring to gigs;
2 1x15 main speakers (some kind of EV)
2 speaker stands fo rthe mains
2 monitors
2 power amps (one for mains, one for monitors) in a six space skb rack
a mackie 16 channel board in an skb case
another six space skb case with a power conditioner, two delay units (one set for reverb, one set for "echo"), a quad compressor, and a stereo 31 band graphic eq for the monitors
4 fifty foot speaker cables
a 12 channel 50' snake
2 sm58 vocal mics, 3 sm57 instrument mics, 1 akg bass drum mic, 3 sennheiser clip on drum mics
2 mic stands with booms and 4 mini mic stands
a direct box
at least 10 mic cables (some as long as 50 feet)
a bunch of heavy duty power cables and power strips sp we can get power no matter how far from the stage the power is
soem rubber mats to cover the snake and power cables so people don't trip and sue us or the venue
a bunch of patch cables to connect stuff.
all the cables are in a couple of rubbermaid containers and they are heavy
we don't always mic the drums or use all 3 instrument mics (it depends on how many amps he brings - wer'e a trio) we also don't usually run my bass into the direct box into the pa either. FYI, he also usually brings a small set of lights, but that's another story. In the case of doing sound for bigger venues and several bands we may bring two subs, a third power amp to run them and a crossover in yet anothe skb case, lots more mics and mic stands, more direct boxes for keys and such, more lights, a longer snake, two more monitors, and a heck of a lot more cords.
like i said, youdont need to jump in and get anything that involved, but having played with a bunch of bands that owned pa setups, i can say that there arent too many things i would take out of our current setup if we had to. maybe using 1x12 mains, smaller monitors, ditching the delay units, using one power amp with one channel for mains and one for monitors, and not bringing the direct box and drum mics. even with all tha tgone a pa is still a big and expensive item