My installer just replaced my oval 3-LNB dish with a new MPEG4 5-LNB dish and we discovered that it DOES NOT WORK with existing receivers. So my HD-Tivo and SD-Directivo do not work with MPEG4-compatible dish. You have to upgrade to the new non-TiVo equipment. He had to climb back up on the roof and remove it.
The new 5-LNB dish works just fine (repeat, WORKS FINE) with all existing equipment. Your installer both made some mistake, and didn't know what he/she was doing, period.
Sorry you got misinformation from the inept installer, but I guess that's all too common.
The new dish also works just fine with existing multiswitches - it just looks like a 3-LNB dish to them. You need a new multiswitch only if you both need more than 4 outputs and are using the two new LNB's.
In the case of dkellyavs, you are using 4 lines to two DirecTiVo's. Everything should work just fine, and the installer either had a bad dish or bad training or bad kharma or ....