```python
def hex_groups(values: list, width: int) -> str:
    if not isinstance(values, list):
        raise ValueError("Input must be a list.")
    if not all(isinstance(x, int) and 0 <= x <= 255 for x in values):
        raise ValueError("All elements must be integers between 0 and 255.")
    if not isinstance(width, int) or width <= 0:
        raise ValueError("Width must be a positive integer.")
    
    hex_values = [format(x, '02x') for x in values]
    grouped_values = [hex_values[i:i+width] for i in range(0, len(hex_values), width)]
    return ' '.join(' '.join(group) for group in grouped_values)
```