Dog Hair and the Sofa
Dori,
If you have excessive dog hair on the sofa, the path of least resistance to a clean sofa is to attack it with the Sebo ET-1. Using the turbo tool is like taking a knife to a gun fight, especially if the sofa looks like a polar bear. For some reason the above floor tools and turbo brushes on the German units leave much to be desired. The same with their hoses.
For your Central unit, a Lux, Lindhaus, Riccar, Wessel or Sebo kit serve you well. Motor in the EBK 360 is Chinese vs the 340 which is not. I am not, nor was I ever a Hayden/Cen-Tec nozzle fan.
As for the D4, it is probably the best unit for your application in such a large home. I have one with the ET-1 I like but don't love. Cord length, hose length, and the best power nozzle money can buy are its best features. The attachments are its downside. It is a little clunky in the real world. Very high quality machine and excellent filtration. A good vacuum if you use one hard. It, along with the Moxie, Lux Platinum, Miele Kona/Marin and Rainbow are top shelf. Remember that almost every hospital in America uses a vacuum with a Sebo nozzle. The 12" performs better in the real world than the 15" does.
My feeling is the best unit as far as convenience, weight, performance and quality is the Lux Platinum so if you return the Sebo go there. The OmniFlo nozzle is not quite as aggressive but the machine has significantly more power than both Miele, Sebo and Rainbow and the best quality attachments made like the combo rug/floor tool. You will like the electric Sidekick III and the flexible urethane hose, light ABS wands, and dual HEPA filters with pets. The Moxie series would be my second choice and equally as nice a unit but less money and USA made. It has similar performance to the Lux and bests both Sebo and Miele when it comes to the numbers.
I have had all of these units/combinations mentioned above in my home for a long time. All the nozzles mentioned do a wonderful job and in more than a decade with Lux found all to remove about the same amount of soil from my carpets when used on a regular basis. The key is to do a quck traffic area vacuum daily (10-15 min) and good thorough cleaning once a week. This avoids a situation where you buy carpet by the yard and throw it away by the pound.
Brian