Here is a list of some of the best speakers featuring RAAL tweeters, known for their soundstage, imaging, highs, mids, bass, warmth, and immersive experience, that you should be able to find used for around $750 or less. The list is sequenced from best to least best based on available information:

1. Salk Sound Soundscape 8 - Known for its exceptional soundstage and the smoothness of the RAAL ribbon tweeter. The overall coherence and audio detail make it a top choice for immersive listening experiences. These may be found used but can vary in price.

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2. Ascend Sierra RAAL Towers - Renowned for their cohesive soundstage and vibrant mids, these speakers offer an engaging listening experience. Users have praised their performance in various settings.

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3. JBL 4305P - Although commonly recognized for their clear highs and decent bass, you'll need to find the right deal for a solid pair with RAAL tweeters included or modded.

4. RAAL 64-10X Bookshelf Speakers - These are equipped with a RAAL 64-10X ribbon tweeter and are noted for their detailed sound and midrange performance, making them a good option if you can find them used.

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Please note that pricing can vary significantly in the used market, and not every speaker may be readily available within your budget of $750. It may take some patience to find the best deals.

Sources

RAAL tweeters - AVS ForumSIERRA-2EX V2 CENTER - Ascend AcousticsRAAL Tweeter - Chane Music & CinemaReview: Salk Sound SoundScape 8 Speaker - Audiogon ForumsUpgrade / Comparisons? Ascend Sierra RAAL Towers / Revel ...Bookshelf Speaker Comparison - Reviews - Audiophile StyleBest speaker for soundstage? : r/audiophile - Reddit

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