Low heat alternative to FIRSTWATT J2 ?


Any Gainclone or Class D or battery power alternatives available? I like the crazy good micro dynamics and rhythmic cohesion of the J2. My speakers are 93db full range. Also interested in AMP/DAC combinations like the devialet or NAD D7050 that meet the J2 performance (those 2 mentioned don't)
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@kosst_amojan, have you heard the J2 or F6 ? I am using a Tannoy Turnberry which is 93db efficient. Not really very efficient but still happy with 20 watts SET. The question is, will the J2 sound too relaxed compared to F6 ?
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I know ventilation all around an amp is desired. If one has an open back and side rack space (like this https://www.audioadvisor.com/mobile/prodinfo.asp?number=PGVULRK&variation=EC&gclid=EAIaIQobC...)
would one be fine running the amp on the bottom shelf?  My audiophile room is in my large finished lower level that stays a constant 70 some degrees.