"Cannot convert from bool to system.collections.generic.list<bool>" In what seems to be good code

I am working on a compression algorithm for fun, but while working on a part of the code where I load some data to a class, I get an error, here is the code that gives the error:

    /// <summary>
    /// Loads an amount of bits from the filestream
    /// </summary>
    /// <param name="fs">A file from which to read the bits</param>
    /// <param name="amount">The amount of bits to read from</param>
    /// <param name="firstByte">The first byte from which to read some bits</param>
    /// <param name="firstByteOffset">The offset fot the first byte</param>
    /// <returns>The next byte and its offset in a tuple</returns>
    public Tuple<byte, int> loadBits(ref FileStream fs, int amount, byte firstByte, int firstByteOffset)
    {
        ///The bits to be added to the internal array
        List<bool> toBeAdded = new List<bool>();
        ///Add the first byte's data
        toBeAdded.AddRange(splitList(new List<bool>(convertByte8(firstByte)), firstByteOffset)[1]);
        ///Add the regular data in the center
        for(int i = 0; i!= (int)Math.Floor((double)amount - 1) / 8; i++)
        {
            toBeAdded.AddRange(convertByte8((byte)fs.ReadByte()));
        }
        ///Create a Tuple that contains the last byte and what it should be offsetted by the next time this method is run
        Tuple<byte, int> rtrnVal = new Tuple<byte, int>((byte)fs.ReadByte(), amount - ((int)Math.Floor((double)amount - 1) / 8) * 8);
        ///Add the bits from the last byte
        toBeAdded.AddRange(splitList(new List<bool>(splitList<bool>(/* error here */new List<bool>(convertByte8(rtrnVal.Item1))[0]/* To here */, rtrnVal.Item2))));
        ///Return
        return rtrnVal;
    }

The error is on the second last line of the method. It should just add the last byte's bits with the offset applied. I don't think it's necessary, but here are the two methods that are non-native (As in I made them):

    /// <summary>
    /// Splits a list into 2
    /// </summary>
    /// <typeparam name="T">The type of the list</typeparam>
    /// <param name="inList">The list to be split</param>
    /// <returns>2 List of half the size each</returns>
    public static List<List<T>> splitList<T>(List<T> inList, int splitIndex = 0)
    {
        splitIndex = Math.Abs(splitIndex);
        if (splitIndex == 0)
        {
            List<List<T>> newLists = new List<List<T>>(2);
            newLists[0] = new List<T>((int)Math.Ceiling((double)inList.Count / 2));
            newLists[1] = new List<T>((int)Math.Floor((double)inList.Count / 2));
            for (int i = 0; i != inList.Count; i++)
            {
                if (i > (int)Math.Ceiling((double)inList.Count / 2))
                {
                    newLists[1][i - (int)Math.Ceiling((double)inList.Count / 2)] = inList[i];
                    continue;
                }
                newLists[0][i] = inList[i];
            }
            return newLists;
        }
        else
        {
            List<List<T>> newLists = new List<List<T>>(2);
            newLists[0] = new List<T>(splitIndex);
            newLists[1] = new List<T>(inList.Count - splitIndex);
            for (int i = 0; i != inList.Count; i++)
            {
                if (i > splitIndex)
                {
                    newLists[1][i - splitIndex] = inList[i];
                    continue;
                }
                newLists[0][i] = inList[i];
            }
            return newLists;
        }
    }
    /// <summary>
    /// Converts a byte to 8 bits
    /// </summary>
    /// <param name="inByteA">The byte to be converted to bits</param>
    /// <returns>The 8 bit representation of inByteA</returns>
    static public bool[] convertByte8(byte inByteA)
    {
        bool[] result = new bool[8];
        string a = Convert.ToString(inByteA, 2);
        int temp = 0;
        foreach (char b in a)
        {
            result[temp] = b == '0' ? false : true;
            temp++;
        }
        return result;
    }

Thank you in advance for any errors there may be in my code that you may find.

PS. What does the ? after a variable mean?