The Avantgarde Duo is magical with the Lamm ML2. There are a few things I did to bring up the bass to the level of the mid-horn, both in terms of quantity and quality. But the Lamm adds an extra dimension to the sound that makes the combination sound more like real instruments, especially on small combo jazz. I have lived with variations on this system for about 15 years in a couple different rooms. The speaker definitely benefits from a large room.
I don’t typically play "audiophile" records-- most are standard issue pressings from back in the day. I had a visitor today for whom I played "I Ain’t Superstitious" from a UK EMI/Columbia first press of Truth. He said it made him want to go home and throw away his copy (probably an Epic). With bass supplementation, you can get the texture and tonality of the bass to play like the mid-horns. The other ingredient for me was a change of cartridge- I had the usual suspects over the years- top line Lyra, Airtight. The Koetsu stone bodies add a level of gravitas and dimension to the bass that I have not heard with other cartridges on this system. So, it is more than just the amp-- but I consider the Lamm a necessary, if not sufficient, element of the combination. The bass was, to me, always the issue with the Duo-- in stock form it either sounds anemic or discontinuous. Now, it is all of a piece. And extremely enjoyable, top to bottom.
PS: Sorry, you won't find the Lamm at 5k, but perhaps double that, used.