Amp pairing for Sierra 2 bookshelves and Vtf-1 Mk2

I've been running this pair for a while off of my Bifrost Uber and Yamaha R-S500. I've caught the upgrade bug as it seems that my amp is pretty lo-fi compared to the rest of my setup and I would like to get the most out of my RAAL tweeters. I have seen some pretty good deals on a few amps: Rega Brio-R, an Outlaw rr2125, a Rega Mira 3, and a NAD C352. My budget is $500-600 shipped and I am unable to audition amps. I have no issues routing my speakers through my subwoofer so not having a subwoofer output will not be a big deal. I appreciate any help I can get and thank you for your responses!:):):)

For an even bigger increase in sound quality, you can get a Sys passive for $50 and a regular power amp. Not having a cheap active line stage in the signal path will make a huge difference.
That's an interesting suggestion. Sorry for my ignorance but what exactly would the sys do for the sound quality? Also what would you suggest for power amps?
Its not what the Sys will do, its what it won't to. To make a good sounding active line stage is difficult and costs a lot more money than what your budget allows. The reason for the high cost is due to the fact that the lower the signal voltage, the more sensitive it is to changes, and that makes it more difficult and costly to work with.

So if you're building a system and have limited funds, a trick to get around the low cost active line stage problem, is to just not use one. Use a passive instead. Its basically an unpowered volume control with 2 inputs (The Sys). All it does is control volume when placed between your dac and amp. You don't plug it in because it doesn't have active circuitry. The reason I mention the Sys, is that its made by the same company that makes your dac and I'm sure that both pieces are designed to compliment each other.

There is one thing I want to be clear on. I'm not saying you can't get a good sounding integrated amp in your price range. You can. My suggestion is meant to take the sound quality of a good amp to the next level.

It wouldn't be a bad idea to call the people that makes your dac and ask them about the combo. Aside from naming their company, they have a very good reputation and know what they're doing.
I had the Sierra-2's in my office with a Rega Brio-r. It was a very musical combo I used for over a year. Hours and hours a day, non-fatiguing.

I also owned a Mira 3 that I used with the same monitors when they were Sierra-1's (before the upgrade). I prefer the Brio-r and the Mira 3's are starting to show their age in the marketplace with the output transistors going bad.
So in that sense do you mean for me to forgo a new amp entirely and get the sys to bypass the preamp in the yamaha or to get a good power amp (which I am certainly open to suggestions on) and connect it via the sys?
I agree with zd. Pairing a passive preamp with an amp could give you much better results in your price range. I'd seriouisly look into offerings from class d audio among others.
Right now based on your combined imput I'm debating between a Virtue Audio Two.2 and a Class D Audio SDS 474C/ Maybe 500C + Schiit SYS. Any thoughts on this combo?
My advice would be to try and listen before making a purchase. Although I own a class d amp and feel it is a tremendous value it may not be your cup of tea.
Well I've used a tube amp before for my HE-500's so if it's anything like that it shouldn't be any issue.
I would like two add my two cents.
I currently own a pair of Sierras but they are version 1with the SEAS silk domes tweeter. I bought them dirt cheap of Audiogon and put them in my main system while I finish up a pair of DYI speakers I am building. Currently they are paired with an Exposure 3010s2 stereo amp and Light Speed Attenuator preamp from Tortuga Audio (Used $1600 total), and a Schiit bitfrost dac. The sound is fantastic. Smooth, fast, thumping, with an excellent sound stage. The thing I like best about this system is that when I put on sub par source material the system is forgiving and still very musical.
I have been down your route trying out amps from $400 to $5600 dollars. Just rotated out a Hegel 300. The best advise I can give is find something musical especially if you are on a budget. My experience with Class D amps and treble has not been that stellar. Hypex (not the Ncores) Class D, Nuforce, and ICE power modules all great amps but there not gonna nock your sox off if your looking to get the most out of those RAAL tweeters. I have heard only one exception, there is a DYI amp fully assembled on Amazon it's the
SMSL SA-36A Pro 20WPC TPA3118D2...and its $70 bucks, it has the best treble of any digital based amp I have heard. Besides being limited by its power factor it also has some of the most refined midrange (vocals) I have also heard in my home.
What are your musical tastes?
I have tried or owned a lot of the amps you will be looking at:

Hmm well that's worrisome as I just ordered a Virtue One.3 but for the sake of future upgrades I listen to a wide variety of music. Hip-Hop, Krautrock, Jazz, Electronic, Folk, Punk, Prog-Rock, among other things. I've heard the ONE.3 is comparable to the Nuforce IA 7 V2 so if you've heard that you have an idea of what my system will sound like. I would say that I love mids and highs so the treble news is saddening.
Fear not Jemidy

I also had the Virtue Sensation M901 which is the bigger brother of the One amps.I recall the sound as being smooth, and tonally rich. The amp boogied and had tighter bass than the Nad I had before it. The only thing I didn't like was the sound stage was some what narrowed, but I later found out that was probably due to the older tubes I had installed in the Dodd tube buffer.
Good to hear any recommendations as far as preamps go in the >$500 range? I was going to go with the Schiit SYS passive pre but with your experience you might know something better!