Ideally, I only need a simple SSLSocketChannel. 
I already have a component that reads and writes message over ordinary SocketChannel, but for          
        
Check out Restlet's implementation it may do what you need, and it's all about NIO.
Restlet Engine Javadoc
Specifically the HttpClientCall. SetProtocol(HTTPS) - getResponseEntityChannel returns a ReadableByteChannel (getEntityChannel returns a WriteableByteChannel)
Not sure if this is what you're looking for, but may help... To create SSL/TLS enabled server sockets, I'm currently using code like the following (keystore.jks contains a self signed private/public key pair used for securing confirmation) - clients have a similar trust store which contains the signed certificate with the public key of that pair.
A bit of googling around getting that configured should get you underway.
String keyStorePath = "keystore.jks";
String keyStorePassword = "password";
KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
KeyStore keyStore = new KeyStore();
keyStore.load(new FileInputStream(keyStorePath), keyStorePassword);
keyManagerFactory.init(keyStore, keyStorePassword.toCharArray());
sslContext = SSLContext.getInstance("TLS");
sslContext.init(keyManagerFactory.getKeyManagers(), null, new SecureRandom());
SSLContext sslContext = getServerSSLContext(namespace.getUuid());
SSLServerSocketFactory serverSocketFactory = sslContext.getServerSocketFactory();
// Create sockets as necessary
Jetty has an NIO SSL implementation for their server: SslSelectorChannelConnector. You might want to peek at it for details on what its doing.
There is also an old (but decent) article from O'Reilly that explains the details about NIO + SSL along with example code.
TLS Channel is a simple library that does exactly that: wrapping a SSLContext (or SSLEngine) and exposing a ByteChannel interface, doing the heavy lifting internally.
(Disclaimer: I am the library's main author).