The older Rotel 10xx series amps are somewhat forward and dry sounding with grainy treble and tonally on the cool side of neutral when not paired carefully with the right speakers, upstream components and cables. But the newer and current Rotel 15xx series amps are very different from the older Rotel 10xx series amps. The new 15xx series sounded way better than the older 10xx series amps. All gone those dry grainy treble and cool lean sounding that you hear from the older 10xx series Rotel Amps. The new current 15xx series eg RB-1590, RB-1582 Mkll, RMB-1585 have warm rich dense tonality and fulsome sound with smooth highs and the noise floor is much lower than the older 10xx series Rotel amps. The new current model Rotel amps, especially the RB-1590, RB-1582 Mkll, RMB-1585, are much quieter design than the older 10xx series amps and have much fuller sound than the older 10xx series amps.
However, the Parasound Halo such as the A21, A31, A51 are excellent and IMO are superior to the newer current Rotel 15xx series amps. You should stick with your Parasound Halo A51 amp.
Fyi, Parasound does not make HT preamp surround processor. Parasound only makes stereo preamps. Rotel makes both stereo preamps and multi-channel preamp surround processors (HT processors).
As a matter of fact when building and designing HT preamp processors Rotel is way behind compared to other manufacturers in keeping up with the latest and most up-to-date surround sound formats and codecs as well as latest video processing such as 4k, HDR and stuff. Rotel is always behind in implementing the latest AV or HT technology. Recently Rotel has just implemented supports for Dolby Atmos, DTS-X, 4k, etc in their HT receiver (RAP 1580) and their lower end HT processor (RSP-1576). Rotel has finally caught up with the latest HT formats whereas other manufacturers have done so few years back.
But Rotel amps are great for the money.
However, the Parasound Halo such as the A21, A31, A51 are excellent and IMO are superior to the newer current Rotel 15xx series amps. You should stick with your Parasound Halo A51 amp.
Fyi, Parasound does not make HT preamp surround processor. Parasound only makes stereo preamps. Rotel makes both stereo preamps and multi-channel preamp surround processors (HT processors).
As a matter of fact when building and designing HT preamp processors Rotel is way behind compared to other manufacturers in keeping up with the latest and most up-to-date surround sound formats and codecs as well as latest video processing such as 4k, HDR and stuff. Rotel is always behind in implementing the latest AV or HT technology. Recently Rotel has just implemented supports for Dolby Atmos, DTS-X, 4k, etc in their HT receiver (RAP 1580) and their lower end HT processor (RSP-1576). Rotel has finally caught up with the latest HT formats whereas other manufacturers have done so few years back.
But Rotel amps are great for the money.