That's probably right. I figured certainly after 18 years it was necessary to upgrade. Seems like after all the research I may have saved myself some money (in the short term anyway)
The BB and similar stores reps have given you their opinions that are mostly subjective, and likely based on hearsay to some extent. I suppose you come here for more opinions, or technical information. Many of us have also gone through different upgrade paths and learnt that sound quality depends mostly on:
1) Quality of the source media (recording, mixing, formats such as MP3, CD, Flac, Wave, WMA, AAC, ALAC, DSD, MQA streaming etc etc etc..), garbage in garbage out right?
2) Media players, i.e. Turntables, CD/DVD/BR/Univeral disc players, Digital file audio players (DAP/DACs), network streamers/players.
3) Speakers, ultimately they are the ones that have to produce the sound.
4) Room acoustic characteristics.
5) Amplifiers, in this case, AVRs.
All of the above are important factors but I put them this particular order/priority based on my perception of the point of diminishing return for each, in terms of $, and audibility of the theoretical and measurable differences. So that means ymmv...
Relatively speaking, it is easier to say with confidence that
all else being equal, CD, 24bit/96kHz flac and other high resolution digital formats such as wave and DSD music files could sound different (usually better) than MP3 64 and 128 kbps, but it gets trickier with MP3 320 kbps that could sound the same to many people, depending on the music contents. It is much difficult to tell the difference between DACs, CD players, and amplifiers that are used well within their specified limits. My comments are based on hardware that are on the right side of the point of diminishing return, obvious examples are the comparisons between the MRX, AVR, and SR products you mentioned. I am quite certain that those units will sound the same in a controlled blind test, even just a single blind tests if no sound processing is used.
*Full disclosure
, I do own and have used several Denon AVRs, two Marantz AVPs, one Marantz preamp and two Marantz power amps, as well as one Anthem power amp.
With sound processing, all bets are off, they will sound different, but different people will have different preference so it is still not possible to know which one you would prefer.
Regarding the Marantz "warm" thing, does that mean Denon and Anthem would sound "cool"? If not, then logically speaking, you should avoid Marantz because that would imply processing, and/or tone control, or distortions may still be in effect even when put in pure direct mode!! It is better to get an amp that simply amplify the signal, so that you can make your own adjustments to suit your taste. Based on specs and numerous lab measurements available online, I have seen nothing that would indicate Marantz has built in such hidden sound processing and/or distortions in order to have it's own sound signature.
You have now been told by BB/AV that basically, each of those brands are designed/built to have their own sound. Some of us believe Denon, Marants, and Anthem's design goal should be accuracy, transparency, It is up to you to choose what to believe, and whether you want to take the chance that you will like one brand's sound better than the others. The BB/AV reps are right about one thing, you can't really tell which "sound" you like best, unless you try all of them in your own home and set each up in exactly the same. Even then, it may be hard to tell without an extended session of ABC comparisons. Everything else aside, that's the main reason why I prefer to go by specs and measurements more than user feedback or forum hearsay, except for the objective views on things like heat issues, noises, reliability and features related matters.