I understand you want to keep things simple by using active monitors and I also understand being budget minded. But, if you get active monitors and skip the receiver you are going to make things more difficult for yourself, probably increase your costs, and decrease your upgrade ability.
Reasons you should not opt for Active speakers.
1.) They tend to be expensive, better performance could be achieved by using a similarly constructed and engineered passive speaker at a lower price.
2.) Each set of active speakers will have independant variable gain control, so you would need to adjust the volume of each set seperate from another set if you decide to do surround sound.
3.) Most, especially for the budget minded, active speakers must have the gain adjusted manually on the speakers. You wouldn't be able to adjust the volume from the comfort of your couch are chair.
4.) Connecting a subwoofer will be very frustrating. The subwoofer level will have to be independently adjusted from the active monitors. Level matching will be near impossible to do by ear. (Believe me, it would be more than frustrating, almost as bad as having to adjust two seperate sets of active speakers.
5.) To my knowledge there aren't many completely active center channels, and I would guess they would be expensive if they have them.
6.) No DTS or bass management. (DTS is technically a superior format to Dolby Digital on paper, but in most conditions they are near the same in real performance and depending on the transfer DTS could be worse than DTS or visa versa)
Reasons to get a receiver-
1.) Upgrade ability, you can connect more components to the receiver in the future if it is needed.
2.) Bass management. It allows you to set the speakers to small and relieve the pressure off the receiver if a subwoofer is connected. In this case we would use the internal x-over in the receiver and by-pass the x-over in the subwoofer.
3.) Various processing modes from Dolby Pro Logic IIx, DTS-Neo:6, and the custom processing of the receiver you choose.
4.) As mentioned before, traditional HT speakers are less expensive for their quality.
I hope this helps in your decision. (It also weighs in favor you already have one pair of passive speakers. If you finish getting the rest of the speakers that are timbre matched with your current speakers)
