Hi Lisa,
I too have a severe hearing loss. The Siemen Tek system and my Rexton Cobalt system are basically the same except for price. Tek was introduced November 2008 and Cobalt was January 2009.
The iPod Touch or iPhone is connected to the remote control with a cable that's included. Transmission from the remote control to the hearing aids is through a wireless (Bluetooth) connection. Bluetooth phones, cellular and landline, are also connected through the remote control. The remote control has buttons to answer and hang up calls and a small speaker.
Another small transmitter, also included, has red and white RCA jacks that connect to a TV or stereo sound equipment. The transmitter connects wirelessly to your hearing aids that become headphones. There is a sound button on the transmitter that I'm still exploring. It seems to adjust the quality whereas the remote control can adjust the volume and treble settings
Both the remote device and transmitter have rechargeable batteries and come with two AC charging units. The battery in the remote control is replaceable, but I don't think the transmitter battery can be removed.
Treble and volume settings and programs (5 available) on the hearing aids are changed wirelessly with the remote. The BTE components also have a button that can change 4 of the 5 programs (not the cell or phone program). Volume and treble settings can only be made with the remote control. However, pressing one button on the BTE also changes the other BTE to the same setting. It pairs them automatically.
The sound quality is quite different from my previous hearing aids and it takes a while for adjustment. They provide more high frequency sound that was a pleasant surprise when I listened to a violin concerto on my car radio. I had not been able the string instruments like that for years. The sound can be disconcerting at first since the rattling of paper and similar sounds are now present.
A real bonus is that wind noise has been eliminated as the result of the new design.
The batteries in the hearing aids are smaller #312's and don't last as long as my previous #13's. I get 7 to 9 days depending on how much I listen to TV or or my iPod Touch.
Like all substitute devices, they're not perfect, but way beyond anything I had before.
Hope this helps.
Cheers, DGM