Which used preamp for Halo A21, under $1,000?

So I've had the Coda CLX in my system for a few weeks now, and I couldn't be happier with it. (I'm running it balanced with Mogami 2534 cables to my Halo A21.)Compared to the Anthem, I'm hearing a lot more detail, a deeper and wider soundstage, great instrument separation even at higher listening levels, and all the dynamics that I imagined were to be had from the Halo A21 driving the Alon IIs. I also like that it's neither noticeably warm or at all lean, but rather staking out a perfect (to my ears) middle ground of neutrality. Timlub mentioned that the sound should continue to improve as the CLX burns in, so it appears there's a little more of the same to come.

Hi, dbxdx5!

It's been a few years but I have the same question you had and I thought I'd try to get your attention and ask if you could help guide me with my quest to drive my Halo A21 to new heights. Like you, I think it sounds ok but know it could sound much better. Now that you've had so much experience with this amp, I wonder if you wouldn't mind helping me out? Which pre do you recommend I buy to make my A21 shine?

Thanks!

louie

Not much has changed in my system since my last post, so I don't know how helpful I can be. Other than the addition of the Coda CLX, I've just put the A21 on a maple amp stand with Dayton Audio spikes between the stand and the floor, and replaced the stock power cord with a Quail, a.k.a. the former Jellyfish Iron Lung. I'm still very happy with the sum total: very neutral and balanced top to bottom.

Louie,  take a look at this thread that I did just recently,  its not very long to read through,  it may help a bit. 
Tim

https://forum.audiogon.com/discussions/should-i-switch-preamps