Nismo upgrade??

[280z/300zx]

So I previously owned a touring sport with the BOSE system and rear subwoofer until it was recently totaled. Decided to go with a Nismo as a replacement but would like to upgrade the sound system a little. I'm not a huge audiophile and don't need anything crazy. The stock touring BOSE system was good enough for me, just to give you an idea of where I'm looking to be. I was just wondering if I pulled the subwoofer from my totaled Z is it just a simple plug and play into the NISMO? Are the hook ups already back there? Would it make a difference with the stock NISMO system?

What other options do I have to get a better system. I'm looking to do as minimal as possible. Could I simply just get better speakers or does the whole head unit need to be replaced as well? What are some good basic speakers or systems I should look at keeping in mind I don't want anything too fancy or crazy?

Thanks.