A friend and I got bored, and, long story short, decided to make an over-engineered FizzBuzz in PHP

<?php

interface INumber
{
    public function go();
    public function setNumber($i);
}

class FBNumber implements INumber
{
    private $value;
    private $fizz;
    private $buzz;

    public function __construct($fizz = 3 , $buzz = 5)
    {
        $this->setFizz($fizz);
        $this->setBuzz($buzz);
    }

    public function setNumber($i)
    {
        if(is_int($i))
        {
            $this->value = $i;
        }
    }

    private function setFizz($i)
    {
        if(is_int($i))
        {
            $this->fizz = $i;
        }
    }

    private function setBuzz($i)
    {
        if(is_int($i))
        {
            $this->buzz = $i;
        }
    }

    private function isFizz()
    {
        return ($this->value % $this->fizz == 0);
    }

    private function isBuzz()
    {
        return ($this->value % $this->buzz == 0);
    }

    private function isNeither()
    {
        return (!$this->isBuzz() AND !$this->isFizz());
    }

    private function isFizzBuzz()
    {
        return ($this->isFizz() OR $this->isBuzz());
    }

    private function fizz()
    {
        if ($this->isFizz())
        {
            return "Fizz";
        }
    }

    private function buzz()
    {
        if ($this->isBuzz())
        {
            return "Buzz";
        }
    }

    private function number()
    {
        if ($this->isNeither())
        {
            return $this->value;
        }
    }

    public function go()
    {
        return $this->fizz() . $this->buzz() . $this->number();
    }
}

class FizzBuzz
{
    private $limit;
    private $number_class;
    private $numbers = array();

    function __construct(INumber $number_class, $limit = 100)
    {
        $this->number_class = $number_class;
        $this->limit = $limit;
    }

    private function collectNumbers()
    {
        for ($i=1; $i <= $this->limit; $i++)
        {
            $n = clone($this->number_class);
            $n->setNumber($i);
            $this->numbers[$i] = $n->go();
            unset($n);
        }
    }

    private function printNumbers()
    {
        $return = '';
        foreach($this->numbers as $number){
            $return .= $number . "\n";
        }
        return $return;
    }



    public function go()
    {
        $this->collectNumbers();
        return $this->printNumbers();
    }


}

$fb = new FizzBuzz(new FBNumber());

echo $fb->go();

In theory, what could we/would you do to make it even more "over-engineered"?