It all depends on the room and what part the extra speakers are intended for, for front ideally all the same speakers, the rears and sides not as important for matching speakers, the DSP3100 and the DSP33 are more then adequate for rears and sides and have the benefit of being able to be suspend by brackets from walls or ceilings.

Good deals can be had for the older legacy speakers here or on eBay but yes DSP5000 and the DSP33 are at present cheaper then the 3100's

Gerard

Home Theater: LG 4K C7, HD621, G61RSL, Oppo 203, MS600, DSP3100 L & R, 2x3100's centers and 4xDSP3100's surrounds. 2x REL S3 SHO and 2x REL habitat1 subwoofers.
Music & TV: Sony 4k XBR 65", Oppo 203, HD621, G68D, C15, 588, M10, M20's, M33's, 4xDSP33's
MD600, 2xTwinStores.. 2xMS600, F80, Prime headphone and PSU.