Is upgrading pre worth it?

Are good preamplifier is always going to improve your system. It's like the heart of it all.

A word to the wise about passive preamps (about which I've done much research and had some real life experience):

1 - Passive preamps, in return for their simplicity & purity of signal path, expose you completely to potential impedance mismatches and/or gain mismatches between the specific & your system. Without trying a given passive unit or doing calculations of voltage & impedance values in your system (in front of & downstream of the passive)--taking into account interconnect length and capacitance--you cannot be certain you won't encounter any impedance or gain mismatch with your system.

2 - I own two passive preamps. Once cost ~$100 & uses transformers. It should sound terrible, but actually sounds quite good, nearly as good as a medium-grade active preamp. There's no detectable bass drop-off; no increase in treble peakiness/brightness; and plenty of volume at reasonable settings. The other is rather expensive (costing 5 times what the cheaper unit costs) & built like a tank by a well known mfr; it uses a very high-grade stepped potentiometer. It sounds awful in my system, with bass clearly lessened, treble clearly brighter, and I have to turn it alarmingly high to get satisfactory volume (that's a bad sign w/a passive).

I believe that, purely by chance, the cheaper passive has neither an impedance mismatch nor gain mismatch in my system, while the far more expensive one has both. It's the luck of the draw...

My advice is simple: if you want to try passives, start small money-wise and try 1 of these 2:

A. Luminous Audio Matrix II Passive: for ~$225, you get a passive built to match your systems specifications (in the order process, you specify key system specs that help assure the unit will not mismatch w/your system). That's very intelligent and helps prevent buyer's remorse. This is a very well-reviewed & well-liked unit; or

B. Tisbury Mini Passive: This British-made unit (easily available from the mfr on eBay for ~$130) has 3 gain settings, an invaluable feature to prevent gain mismatches. It's not fancy, but many like the sound.

Fortunately, the Creek OBH-22 seems to match most of my equipment pretty well - so, it is a bargain for me - though, I’ve not tried it with all of my various speakers, amps and sources.

Not an EE but, I agree - Impedence, gain and current matching is a critical factor in attaining the best sound from your components. I became aware of impedence and gain matching, with some headphone amps I have / had.

I wondered why the X-CAN v3 would sound great with my high impedence phones and less so, with my low impedence phones, while the X-CAN v8 just the opposite. It turned out to be an impedence matching issue. Makes all the difference.

Truly cheap passive, Schiit SYS, $50 + shipping.  I bought one just to play with. Use it with my Dynaco ST-70 amp. 

I got rid of the denon. I got the Rogue pre 99 super magnum. It sounds pretty good. I also bought the Antelope zodiac DAC pre. A hand full of people not knowing what’s what for gear, but with a pretty legit music background thought the Zodiac alone as a pre/dac sounded better than the Rogue pre with the Zodiac working together. This is with cheap speakers. I have Penaudios coming in next week. That will be the real test.. So yea ROGUE ST100 needed a pre, who knew.. The difference is real. 1500 real? Yes I would say so and I like to have my money in my account.