What are you recording?
What (actual or virtual) instruments, apart from vocals, are you recording? How?
What microphone are you using?
Describe the room you're recording in - how big is it? What are the walls made of?
How are you monitoring what you're recording?
The Boss preamps will be fine for now. Generally the first answer to any query is NOT to buy more stuff. More stuff doesn't necessarily improve things off the bat, although we all like buying more stuff. What you need to do to start with is control the variables you have and work out how to improve your recording, rather than introduce another variable such as a new preamp or microphone.
Once you've ruled out everything else, then you go gear shopping.
You'll hear the same thing over and over again if you ask around - "I bought a new Fandangled Gromulater preamp and my recordings still suck".... yes, that's because you don't know how to position your microphone and you're recording in a small square echoey room and you're monitoring via headphones, perhaps. Work with what you have for now is my advice.
I recorded 3 entire albums on standalone machines - bigger than yours, but still, they're largely the same thing. It can be done. Many here will tell you the same thing.