How to display PowerShell Results in Textboxes

Just split your string into an array or list and then assign them to the textboxes.

            using (PowerShell powerShell = PowerShell.Create())
            {
                powerShell.AddScript("Get-ComputerInfo | Select-Object CsDNSHostName,WindowsProductName, OSVersion, CSDomainRole, CSProcessors, OsProductType");
                powerShell.AddCommand("Out-String");
                Collection<PSObject> PSOutput = powerShell.Invoke();
                StringBuilder stringBuilder = new StringBuilder();
                foreach (PSObject pSObject in PSOutput)
                    stringBuilder.AppendLine(pSObject.ToString());
                var stringarr = stringBuilder.ToString().Split(Environment.NewLine.ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
                textBox1.Text = stringarr[0];
                textBox2.Text = stringarr[1];
                textBox3.Text = stringarr[2];
                textBox4.Text = stringarr[3];
                textBox5.Text = stringarr[4];
                textBox6.Text = stringarr[5];
            }

One quite note you might like for future usage.
If you add/change ConvertTo-Json + Newtonsoft.Json to your project you can easily phrase the string output (JSON Formated) to a class.

1. Change Out-String to ConvertTo-Json

powerShell.AddCommand("ConvertTo-Json");

2. Stop in debug once after Clipboard.SetText(stringBuilder.ToString());

3. Use Visual Studio Menu -> Edit -> Paste Special -> Paste JSON as Classes

Full code to phrase your output to a class.

 private void button1_Click(object sender, EventArgs e)
        {
            using (PowerShell powerShell = PowerShell.Create())
            {
                powerShell.AddScript("Get-ComputerInfo | Select-Object CsDNSHostName,WindowsProductName, OSVersion, CSDomainRole, CSProcessors, OsProductType");
                powerShell.AddCommand("ConvertTo-Json");
                Collection<PSObject> PSOutput = powerShell.Invoke();
                StringBuilder stringBuilder = new StringBuilder();
                foreach (PSObject pSObject in PSOutput)
                {
                    stringBuilder.AppendLine(pSObject.ToString());
                }
#if DEBUG
                Clipboard.SetText(stringBuilder.ToString());
#endif
                Rootobject retval = JsonConvert.DeserializeObject<Rootobject>(stringBuilder.ToString());

                textBox1.Text = retval.CsDNSHostName.Trim();
                textBox2.Text = retval.WindowsProductName.Trim();
                textBox3.Text = retval.OsVersion.Trim();
                textBox4.Text = retval.CsDomainRole.ToString();
                textBox5.Text = retval.CsProcessors[0].Description.Trim();
                textBox6.Text = retval.OsProductType.ToString();
            }
        }


        public class Rootobject
        {
            public string CsDNSHostName { get; set; }
            public string WindowsProductName { get; set; }
            public string OsVersion { get; set; }
            public int CsDomainRole { get; set; }
            public Csprocessor[] CsProcessors { get; set; }
            public int OsProductType { get; set; }
        }

        public class Csprocessor
        {
            public string Name { get; set; }
            public string Manufacturer { get; set; }
            public string Description { get; set; }
            public int Architecture { get; set; }
            public int AddressWidth { get; set; }
            public int DataWidth { get; set; }
            public int MaxClockSpeed { get; set; }
            public int CurrentClockSpeed { get; set; }
            public int NumberOfCores { get; set; }
            public int NumberOfLogicalProcessors { get; set; }
            public object ProcessorID { get; set; }
            public object SocketDesignation { get; set; }
            public object ProcessorType { get; set; }
            public string Role { get; set; }
            public string Status { get; set; }
            public int CpuStatus { get; set; }
            public int Availability { get; set; }
        }

I usually use this methode to invoke a script.

public List<object> InvokeScript(string script)
        {

            List<object> pSDataStreams = new List<object>();
            using (PowerShell powerShell = PowerShell.Create())
            {
                powerShell.Streams.Information.DataAdding += (sender, e) => { pSDataStreams.Add(e.ItemAdded); };
                powerShell.Streams.Error.DataAdding += (sender, e) => { pSDataStreams.Add(e.ItemAdded); };
                powerShell.Streams.Debug.DataAdding += (sender, e) => { pSDataStreams.Add(e.ItemAdded); };
                powerShell.Streams.Progress.DataAdding += (sender, e) => { pSDataStreams.Add(e.ItemAdded); };
                powerShell.Streams.Verbose.DataAdding += (sender, e) => { pSDataStreams.Add(e.ItemAdded); };
                powerShell.Streams.Warning.DataAdding += (sender, e) => { pSDataStreams.Add(e.ItemAdded); };

                powerShell.AddScript(script);

                // powerShell.Streams.Information.d
                using (var outputCollection = new PSDataCollection<PSObject>())
                {
                    outputCollection.DataAdding += (sender, e) => { pSDataStreams.Add(e.ItemAdded); };
                    powerShell.Invoke(null, outputCollection);
                }
            }
            return pSDataStreams;
        }